COSMO: Conductor-like Screening Model
*************************************

You can study chemistry in solution, as contrasted to the gas phase,
with the implementation in ADF [1] of the Conductor-like Screening
Model (COSMO) of solvation [2] [3] [4]. The energy derivatives can
also be calculated, so geometry optimization, harmonic frequencies, et
cetera are available within this model.

The COSMO model is a dielectric model in which the solute molecule is
embedded in a molecule-shaped cavity surrounded by a dielectric medium
with given dielectric constant \epsilon. Energy-related terms are
computed for a conductor first, then scaled by the function

   f(\epsilon) = \frac{\epsilon-1}{\epsilon + x} \qquad (2.1.1)

The empirical scaling factor *x* is specified in the input data block
for the SOLVATION key. The block key SOLVATION turns the solvation
calculation on. In most cases, default values are available for the
involved parameters. In order to construct the cavity, atomic cavity
radii are used. The default COSMO atomic cavity radii used in ADF are
the Van der Waals radii from the MM3 method by Allinger (Ref. [5])
divided by 1.2.

It is also possible to include a linear parametrization of non-
electrostatic terms as a function of surface area. To include such a
term, specify it in the input data block for the SOLVATION key. The
default is to include only the part of this term that is proportional
to the surface area (default CAV0=0.0, CAV1=0.0067639):

   E_\text{non-elst} = f(\epsilon) (CAV0 + CAV1 \times \text{area})
   \qquad  (2.1.2)

If a calculation is performed on a fragment, the resulting wave
function is optimal for the fragment in solution, but not for the gas
phase. The energies with the gas-phase Hamiltonian are then higher,
and the apparent solvation contribution to bonding is also higher. In
practice, the COSMO procedure reports the energy Esolv(AB), but to
obtain the solvation energy, you need to subtract E(AB, solv) from
E(AB, gas), because the wave function changes, unless you are doing
this post-SCF. For this, you need to use the same reference fragments
in each case, A(g) and B(g).

Because of precision issues in ADF2016, the default surface has been
changed to Delley instead of Esurf.

   SOLVATION
    {SURF Surface {NOKEEP}}
    {SOLV {Name=solvent} {Eps=78.4} {Del=1.4} {Rad=1.4}
          {Neql=1.9}{Emp=0.0}{Cav0=0.0}{Cav1=0.0067639} }
    {DIV {Ndiv=3} {NFdiv=1} {Min=0.5} {OFAC=0.8}
         {leb1=23} {leb2=29}{rleb=1.5} }
    {NOASS}
    {RADII
      name1=value1
      name2=value2
      ...
    End }
    {CHARGED {Method=meth} {Conv=1e-8} {Omega=1.0} {Iter=1000}
             {Corr} {LoCosmo LoCosmoDist}}
    {C-MAT How {SCF} tol=1e-10 }
    {DISC {SC=0.01} {LEG=4} {TOL=0.1} }
    {SCF {When} {How}
    {NOCSMRSP}
    {LPRT}
   End

Presence of the SOLVATION key block triggers the solvent calculation
and does not require additional data. With subkeys you can customize
various aspects of the model, for instance to specify the type of
solute. None of the subkeys is obligatory. A description of the
subkeys follows.

"SURF Surface {NOKEEP}"
   Defines the type of cavity to be used. "Surface" can be one of the
   following: Wsurf, Asurf, Esurf, Klamt, or Delley. **Default:
   Delley**. The Wsurf, Asurf, and Esurf surfaces are constructed with
   the GEPOL93 algorithm [6].

   "Wsurf"
      Wsurf triggers the Van der Waals surface (VdW), which consists
      of the union of all atomic spheres. Not recommended.

   "Asurf"
      Asurf gives the Solvent-Accessible-Surface (SAS). This is
      similar to VdW but consists of the path traced by the center of
      a spherical solvent molecule rolling about the VdW surface or,
      equivalently, a VdW surface created by atomic spheres to which
      the solvent radius has been added. These two surface types
      contain cusps at the intersection of spheres. Not recommended.

   "Esurf"
      Esurf gives the Solvent-Excluding-Surface (SES), which consists
      of the path traced by the *surface* of a spherical solvent
      molecule rolling about the VdW surface. Primarily, this consists
      of the VdW surface but in the regions where the spheres would
      intersect, the concave part of the solvent sphere replaces the
      cusp.

   "Klamt"
      The fourth surface option is Klamt as described in [2]. It also
      excludes the cusp regions. Note that this surface might give an
      incomplete COSMO surface for more complicated molecules. Not
      recommended.

   "Delley"
      The fifth surface (default surface) is the so-called Delley
      surface, see also Ref. [7]. This Delley type of cavity
      construction is recommended for COSMO calculations whose results
      are used as input for COSMO-RS calculations; see the
      corresponding manual for COSMO-RS. This Delley surface is the
      default COSMO surface in ADF.

"DIV"
   The actual construction of the surface involves a few technical
   parameters controlled with the subkey DIV.

   "Ndiv, NFdiv"
      Ndiv controls how finely the spheres that describe the surface
      are partitioned into small surface triangles, each containing
      one point charge to represent the polarization of the cavity
      surface. Default division level for triangles Ndiv=3. Default
      final division level for triangles NFdiv=1 (NFdiv \leq Ndiv).
      Not used in the Delley surface.

   "Min"
      Min specifies the size, in Angstrom, of the smallest sphere that
      may be constructed by the SES surface. For VdW and SAS surfaces
      it has no meaning. Default Min=0.5. Not used in the Delley
      surface.

   "Ofac"
      Ofac is the maximum allowed overlap of newly created spheres in
      the construction procedure. Default Ofac=0.8. Not used in the
      Delley surface.

   "leb1, leb2, rleb"
      Only used in the Delley surface. For the Delley type of
      construction one needs to set the variables leb1 (default value
      23), leb2 (default value 29), and rleb (default value 1.5
      Angstrom) to set the number of surface points. If the cavity
      radius of an atom is lower than rleb, use leb1; otherwise, use
      leb2. These values can be changed: using a higher value for leb1
      and leb2 gives more surface points (maximal value leb1, leb2 is
      29). A value of 23 means 194 surface points in the case of a
      single atom, and 29 means 302 surface points in the case of a
      single atom. Typically one could use leb1 for the surface point
      of H, and leb2 for the surface points of other elements.

"NOASS"
   By default all new spheres that are created during surface
   construction are assigned to atoms, for the purpose of gradient
   computations (geometry optimization). Specifying the noass subkey
   turns this off. It has no argument.

"SOLV"
   Solvent details.

   "Eps, Rad"
      Eps specifies the dielectric constant (the default relates to
      water). In ADF an infinite value for Eps is chosen if Eps is
      specified to be lower than 1.0. Rad specifies the radius of the
      (rigid sphere) solvent molecules, in Angstrom. Instead of
      specifying Eps and Rad, one can specify a solvent name or
      formula after 'name='. The following table lists names and
      formulas that are recognized with the corresponding values for
      Eps and Rad. The Rad in this table is calculated from the
      density, the molar mass, and a spherical approximation for the
      solvent. The names and formulas are case-insensitive.

      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Name                      | Formula                   | Eps                       | Rad                       |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | AceticAcid                | CH3COOH                   | 6.19                      | 2.83                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Acetone                   | CH3COCH3                  | 20.7                      | 3.08                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Acetonitrile              | CH3CN                     | 37.5                      | 2.76                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Ammonia                   | NH3                       | 16.9                      | 2.24                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Aniline                   | C6H5NH2                   | 6.8                       | 3.31                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Benzene                   | C6H6                      | 2.3                       | 3.28                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | BenzylAlcohol             | C6H5CH2OH                 | 13.1                      | 3.45                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Bromoform                 | CHBr3                     | 4.3                       | 3.26                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Butanol                   | C4H9OH                    | 17.5                      | 3.31                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | isoButanol                | (CH3)2CHCH2OH             | 17.9                      | 3.33                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | tertButanol               | (CH3)3COH                 | 12.4                      | 3.35                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | CarbonDisulfide           | CS2                       | 2.6                       | 2.88                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | CarbonTetrachloride       | CCl4                      | 2.2                       | 3.37                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Chloroform                | CHCl3                     | 4.8                       | 3.17                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Cyclohexane               | C6H12                     | 2                         | 3.5                       |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Cyclohexanone             | C6H10O                    | 15                        | 3.46                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Dichlorobenzene           | C6H4Cl2                   | 9.8                       | 3.54                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | DiethylEther              | (CH3CH2)2O                | 4.34                      | 3.46                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Dioxane                   | C4H8O2                    | 2.2                       | 3.24                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | DMFA                      | (CH3)2NCHO                | 37                        | 3.13                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | DMSO                      | (CH3)2SO                  | 46.7                      | 3.04                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Ethanol                   | CH3CH2OH                  | 24.55                     | 2.85                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | EthylAcetate              | CH3COOCH2CH3              | 6.02                      | 3.39                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Dichloroethane            | ClCH2CH2Cl                | 10.66                     | 3.15                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | EthyleneGlycol            | HOCH2CH2OH                | 37.7                      | 2.81                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Formamide                 | HCONH2                    | 109.5                     | 2.51                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | FormicAcid                | HCOOH                     | 58.5                      | 2.47                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Glycerol                  | C3H8O3                    | 42.5                      | 3.07                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | HexamethylPhosphoramide   | C6H18N3OP                 | 43.3                      | 4.1                       |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Hexane                    | C6H14                     | 1.88                      | 3.74                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Hydrazine                 | N2H4                      | 51.7                      | 2.33                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Methanol                  | CH3OH                     | 32.6                      | 2.53                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | MethylEthylKetone         | CH3CH2COCH3               | 18.5                      | 3.3                       |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Dichloromethane           | CH2Cl2                    | 8.9                       | 2.94                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Methylformamide           | HCONHCH3                  | 182.4                     | 2.86                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Methypyrrolidinone        | C5H9NO                    | 33                        | 3.36                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Nitrobenzene              | C6H5NO2                   | 34.8                      | 3.44                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Nitrogen                  | N2                        | 1.45                      | 2.36                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Nitromethane              | CH3NO2                    | 35.87                     | 2.77                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | PhosphorylChloride        | POCl3                     | 13.9                      | 3.33                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | IsoPropanol               | (CH3)2CHOH                | 19.9                      | 3.12                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Pyridine                  | C5H5N                     | 12.4                      | 3.18                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Sulfolane                 | C4H8SO2                   | 43.3                      | 3.35                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Tetrahydrofuran           | C4H8O                     | 7.58                      | 3.18                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Toluene                   | C6H5CH3                   | 2.38                      | 3.48                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Triethylamine             | (CH3CH2)3N                | 2.44                      | 3.81                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | TrifluoroaceticAcid       | CF3COOH                   | 8.55                      | 3.12                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+
      | Water                     | H2O                       | 78.39                     | 1.93                      |
      +---------------------------+---------------------------+---------------------------+---------------------------+

   "Del"
      Del is the value of Klamt's delta_sol parameter, only relevant
      in the case of the Klamt surface.

   "Neql"
      If Neql = \epsilon_NEQL  is included, non-equilibrium solvation
      is used, i.e. the dielectric constant \epsilon_NEQL  used in
      RESPONSE is different from the ground-state dielectric constant
      \epsilon. Only relevant in the case of TDDFT calculations.
      Default \epsilon_NEQL  = \epsilon. The reason for using two
      different dielectric constants is that the electronic transition
      can be so fast that only the electronic component of the solvent
      dielectric can respond, i.e., one should use the optical part of
      the dielectric constant. This is typically referred to as non-
      equilibrium solvation. The optical dielectric constant can be
      obtained from the (frequency-dependent) refractive index n of
      the solvent as \epsilon_NEQL  = n^2.

   "Emp"
      Emp addresses the empirical scaling factor *x* in the formula
      2.1.1 above.

   "Cav0, Cav1"
      Other options specify a linear parametrization of non-
      electrostatic terms as a function of surface area; see formula
      2.1.2 above. Possible values for CAV0 and CAV1 are CAV0 = 1.321
      and CAV1 = 0.0067639, see Ref. [8]. In ADF2010 the default
      values for CAV0 and CAV1 are CAV0 = 0.0 and CAV1 = 0.0. However,
      starting from ADF2012 the default values for CAV0 and CAV1 are
      CAV0 = 0.0 and CAV1 = 0.0067639. If CAV0 is not zero, Esolv(AB)
      is not the same as Esolv(A) + Esolv(B) if A and B are far apart.
      This is the reason why CAV0 is set to zero by default. By
      default, CAV1 is not set to zero; thus there is a solvation
      energy term that does depend on the size of the cavity (surface
      area).

"COSMO Radii"
   In order to construct the surface you have to specify the atomic
   ('Van der Waals') radii. There are three ways of doing this. In the
   first method you append 'adf.R=value' to the atomic coordinates
   record, in the ATOMS key block. For instance, this would look like:

      C 1 2 3 CC CCO CCOH adf.f=C.dz adf.R=2.0

   It assigns a radius of 2.0 to the Carbon atom. In the second method
   you apply the same format, but specify a symbol (identifier) rather
   than a value:

      C 1 2 3 CC CCO CCOH adf.f=C.dz adf.R=C-sp3

   The identifiers must be defined in the (optional) RADII subkey
   block in the Solvation data block (see next). In the third method,
   you do not modify the Atoms block at all. In this case, the RADII
   subkey must be used and the 'identifiers' in it must be exactly the
   atom type names in the Atoms block.

"RADII"
   This subkey is of block type. Its data block (if the subkey is
   used) must terminate with a record End. In the Radii data block you
   give a list of identifiers and values:

      SOLVATION
         ...
         Radii
            name1=value1
            name2=value2
            ...
         End
         ...
      End

   The values are the radii of the atomic spheres, in the same length
   units as used in the Atoms block (Angstrom or bohr). The names
   specify to which atoms these values apply. As discussed for the
   Solv subkey, this depends on the Atoms block. If in the
   specification of atomic coordinates you have used the 'adf.R='
   construct to assign radii, with identifiers rather than values for
   the R-value, these identifiers must be defined in the Radii sub
   block. If no 'adf.R=' construct was applied in the Atoms block, you
   must use the atom type names as they occurred in the Atoms data
   block. Referring to the example given in the Solv subkey
   discussion, you might have:

      Radii
         C-sp3=2.0
         ...
      End

   A simple atom type reference might look like:

      Radii
         C=2.0
         ...
      End

   When no radius is specified a default value is used. The default
   value for an atom is the corresponding Van der Waals radius from
   the MM3 method by Allinger (Ref. [5]) divided by 1.2, see Ref. [9].

   Another popular choice is the so-called Klamt atomic cavity radii
   set (Ref. [10]), which is optimized for a few elements:

      Radii
         H  1.30
         C  2.00
         N  1.83
         O  1.72
         F  1.72
         Si 2.48
         P  2.13
         S  2.16
         Cl 2.05
         Br 2.16
         I  2.32
      End

"CHARGED {Method=meth} {Conv=1e-8} {Omega=1.0} {Iter=1000} {Corr}
{LoCosmo LoCosmoDist}"
   This addresses the determination of the (point) charges that model
   the cavity surface polarization. In COSMO calculations you compute
   the surface point charges *q* by solving the equation A*q*=-*f*,
   where *f* is the molecular potential at the location of the surface
   charges *q* and A is the self-interaction matrix of the charges.
   The number of charges can be substantial and the matrix A hence
   very large. A direct method, i.e. the inversion of A, may be very
   cumbersome or even impossible due to memory limitations, in which
   case you have to resort to an iterative method. Meth specifies the
   equation-solving algorithm. Meth=INVER requests direct inversion.
   Meth=GAUS calls for the Gauss-Seidel iterative method. Meth=Jacobi
   activates another standard iterative procedure. The latter two
   methods require a positive-definite matrix (which may fail to be
   the case in an actual calculation) and can be used with a
   relaxation technique, controlled by the relaxation parameter OMEGA
   (1.0=no relaxation). Meth=CONJ (default) uses the preconditioned
   biconjugate gradient method. This is guaranteed to converge and
   does not require huge amounts of memory. CONV and ITER are the
   convergence criterion and the maximum number of iterations for the
   iterative methods. Some of the molecular electronic charge
   distribution may be located outside the cavity. This affects the
   assumptions underlying the COSMO equations. LOCOSMO can only be
   used in combination with FDE.

   Specifying the CORR option to the CHARGED subkey constrains the
   computed solvent surface charges to add up to the negative of the
   molecular charge. In ADF2016 this outlying charge correction is
   also done during the SCF. Note that before ADF2016 it was only a
   post-SCF correction on the COSMO charges. In ADF2018 a bug that was
   introduced in ADF2016 in case of this outlying charge correction
   was fixed for the energy (typically a small effect).

"C-MATRIX"
   How: For the potential *f* we need the Coulomb interaction between
   the charges *q* and the molecular electronic density (and nuclei).
   Three methods are available, specified by the first option to the
   C-Matrix subkey.

   1. EXACT: compute the straightforward Coulomb potential due to the
      charge *q* in each point of the molecular numerical integration
      grid and integrate against the electronic charge density. This
      is, in principle, exact but may have inaccuracies when the
      numerical integration points are very close to the positions of
      a charge *q*. To remedy this, the point charges *q* can be
      'smeared out' and represented by a disc, see the next subkey
      DISC.

   2. FIT: same as EXACT, but the *q*-potentials are now integrated
      not against the exact electronic charge density, but against the
      (much cheaper-to-compute) fitted density. The same DISC
      considerations apply.

   3. POT: evaluate the molecular potential at the position of the
      charge *q* and multiply against the *q*-strength. Since the
      molecular Coulomb potential is computed from the fit density,
      any difference in results between the FIT and the POT approach
      should be attributed to the DISC issue. POT is the default,
      because it is faster, and is only inadequate if the fit density
      is very inaccurate, which would be a problem anyway.

   SCF: If you specify this option, the computation of the Coulomb
   interaction matrix (between electrons and surface charges) is
   carried out during the SCF procedure, but this turns out to hamper
   the SCF convergence behavior. Therefore: not recommended. *IF* you
   use it, the program will switch to one of the other three methods,
   as given by the 'How' option, as soon as the SCF convergence error
   drops below TOL: (applies only to the SCF option, which is not
   recommended).

"DISC"
   Applies only when the C-matrix method is EXACT or FIT. Note,
   however, that the default for the C-matrix method is POT, in which
   case the DISC subkey has no meaning. The DISC key lets the program
   replace the point charges *q* by a solid uniformly charged
   spherical surface disc whenever required by the numerical
   integration accuracy, i.e. for those charges that are close to
   numerical integration points. Options: SC defines a shrinking
   factor, by which the actual disc radius used is reduced from its
   'normal' value: an inscribed disc in the triangular surface
   partitions that define the distribution of surface charges, see the
   subkey DIV. LEG gives the polynomial expansion order of the disc
   potentials. The Legendre expansion converges rapidly and the
   default should be adequate.

   TOL is a tolerance parameter to control the accuracy of the disc
   potential evaluations.

"SCF"
   In COSMO calculations you can include the surface charges in the
   Fock operator self-consistently, i.e. by recomputing the charges
   *q* at every SCF cycle and include them in the equations, or in a
   perturbational manner, i.e. post-SCF. This is controlled with the
   first option. The When option must be either VAR or PERT, for
   variational and perturbational, respectively. Default is VAR. The
   second (HOW) option applies only to the WHEN=VAR case and may
   affect the speed of SCF convergence. The COSMO calculation implies
   a considerable increase in CPU time! Values for HOW:

   * ALL: This includes it in all SCF cycles (except for the first SCF
     cycle, which is gas-phase)

   * LAST: This lets the program first converge the SCF completely
     without any solvent effects. Thereafter, the COSMO is turned on,
     hopefully converging in fewer cycles now, to compensate for the
     'double' SCF effort.

   * TOL=0.1 (or another value) is an in-between approach: converge
     the gas-phase SCF until the SCF error is below TOL, then turn on
     COSMO.

"NOCSMRSP"
   Relevant only in combination with the time-dependent DFT (TDDFT)
   applications: the EXCITATIONS, the RESPONSE, or the AORESPONSE key.
   If the NOCSMRSP subkey is included, the induced electronic charges
   that are present in the TDDFT calculations will not influence the
   COSMO surface charges. No dielectric constant in the response might
   be closer to the optical dielectric constant than using the full
   dielectric constant, see also sub-argument NEQL of the subkey SOLV
   of the key SOLVATION. By default, in the absence of this subkey
   NOCSMRSP, the induced electronic charges will influence the COSMO
   surface charges. If one does geometry optimization of the excited
   state, this makes sense, since then the solvent dielectric has time
   to fully respond.

"LPRT"
   This is a debug switch and triggers a lot more output related to
   cavity construction and related details.

**Warning**

Numerical frequencies calculated with COSMO should be checked for
stability with respect to the NumericalDifferentiation%NuclearStepSize
in the AMS part of the input, the numerical differentiation step size.
The problem is that the COSMO surface changes slightly when a nucleus
is moved from its equilibrium position. The change is usually small,
but in some cases it may result in the creation or annihilation of
surface points, which will lead to discontinuities in the potential
energy surface and may result in inaccurate frequencies.

Thus, when calculating vibrational frequencies numerically with COSMO,
one should try decreasing the NumericalDifferentiation%NuclearStepSize
value in the AMS part of the input, until no changes in frequencies
are observed. However, the value should not be too small because then
the total numerical noise may become too large compared to the
generated forces. A general recommendation would be to try to decrease
NuclearStepSize by a factor of 2 at a time. Of course, this procedure
may be very expensive for a large molecule. If this is the case, one
could use the NormalModes%ReScanModes or NormalModes%ReScanFreqRange
in the AMS part of the input, in order to recalculate frequencies
along a normal mode. It should be noted that generally frequencies
that have a small force constant are more sensitive to the numerical
noise.

[1] C.C. Pye and T. Ziegler, *An implementation of the conductor-like
    screening model of solvation within the Amsterdam density
    functional package*, Theoretical Chemistry Accounts 101, 396
    (1999)

[2] A. Klamt and G. Schüürmann, *COSMO: a new approach to dielectric
    screening in solvents with explicit expressions for the screening
    energy and its gradient*, Journal of the Chemical Society: Perkin
    Transactions 2, 799 (1993)

[3] A. Klamt, *Conductor-like Screening Model for real solvents: A new
    approach to the quantitative calculation of solvation phenomena*,
    Journal of Physical Chemistry 99, 2224 (1995)

[4] A. Klamt and V. Jones, *Treatment of the outlying charge in
    continuum solvation models*, Journal of Chemical Physics 105, 9972
    (1996)

[5] N.L. Allinger, X. Zhou, J. Bergsma, *Molecular mechanics
    parameters*, Journal of Molecular Structure: THEOCHEM 312, 69
    (1994)

[6] J.L. Pascual-ahuir, E. Silla and I. Tuñon, *GEPOL: An improved
    description of molecular surfaces. III. A new algorithm for the
    computation of a solvent-excluding surface*, Journal of
    Computational Chemistry 15, 1127 (1994)

[7] B. Delley, *The conductor-like screening model for polymers and
    surfaces*, Molecular Simulation 32, 117 (2006)

[8] T.N. Truong and E.V. Stefanovich, *A new method for incorporating
    solvent effect into the classical, ab initio molecular orbital and
    density functional theory frameworks for arbitrary shape cavity*,
    Chemical Physics Letters 240, 253 (1995)

[9] M. Swart, E. Rösler, F.M. Bickelhaupt, *Proton Affinities in Water
    of Maingroup-Element Hydrides - Effects of Hydration and Methyl
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