Second List

ALLBANDS

Requires a numerical argument, which is an energy width, in a.u.. It simulates a finite-temperature electronic distribution. By default, zero temperature is assumed. The key may be used to achieve convergence in an otherwise problematically converging system (slabs, typically). The energy of a finite-T distribution is different from the T=0 value, but for small T a fair approximation of the zero-T energy is obtained by extrapolation. The extrapolation energy correction term is printed with the survey of the bonding energy in the output file. Check that this value is not too large. Build experience yourself how different settings may affect the outcomes. Remember that this key is meant to help you overcome convergence problems, not to do finite-T research: only the electronic distribution is computed T-dependent, other aspects are not accounted for!

ALWAYSNLPOT

If a GGA (Generalized Gradient Approximation) is used in the density functional, applying it is by default suppressed in the early stages of the SCF procedure, to save CPU time (the evaluation of GGA potentials may be rather time consuming). Using this key cancels this feature so that any GGA is evaluated at every cycle of the SCF, including the initial ones.

BASISDEPEND

Criterion for dependency of the valence basis set (smallest eigenvalue of the overlap matrix of normalized bloch functions). Default 1e-5. See also the discussion in "Recommendations & Problems" about basis set dependency.

BOLTZMAN

Number of points by which the finite temperature Fermi-Dirac distribution of electronic occupations is approximated. Advise: don't use.

CHECKBASCOROVL

Check the dependency of the valence basis on the frozen core orbitals, by analysis of the core-valence overlap matrix. Since this takes some CPU time, it is by default off.

CONTINUE

debugging feature to let the program continue even when intermediate results seem to be wrong or very inaccurate. Currently there are only few places in the program where this key is used.

CONVERGENCE

Criterion for termination of the SCF procedure. Default depends on ACCINT, for instance 3e-4 for accint=4.0

COREDEPEND

The program verifies that the frozen core approximation is reasonable, by checking the smallest value of the overlap matrix of the core (bloch) orbitals against this criterion. Default: 0.98

COREFUNC

use Slater type auxiliary functions to enforce that valence basis functions are orthogonal to all core orbitals. By default this is achieved by explicitly (numerically) projecting out the component of the core orbitals from the valence functions. This key is currently disabled.

COREVALENCEDEPEND

Criterion for dependency of the core functions on the valence basis. The maximum overlap between any two normalized functions in the two respective function spaces should not exceed 1.0-COREVAL(...). DEFAULT 1E-5.

CPVECTOR

Maximum vector length in vector operations. Default depends on the machine, and should be set at the installation of the program at your site.

CUTMIN

A confinement approach has been implemented in BAND to squeeze the radial atomic functions a bit faster to zero. This is achieved through multiplication by a confinement function that drops to zero between a turn-on radius and a turn-off radius. CUTMIN is the lower r-value. Default 12.0
Obviously, confinement of functions may have some impact on the numerical outcomes. The defaults have been chosen to make this effect very small. It doesn't hurt, of course, to experiment a little bit and get more feeling for the effects.

CUTMAX

See CUTMIN. CUTMAX is the higher r-value. Beyond this, all radial basis functions are forcibly zero Default 16.0

CUTOFF

Criterion for negligibility of tails in the construction of Bloch sums. Default depends on ACCINT.

CYCLES

The maximum number of SCF iterations to be performed. If zero (default value) termination of the SCF procedure will depend only on other aspects (convergence, time-out, insufficient progress towards convergence...)

DEBUG

Induces extra printing and sets up the key CONTINUE

DEBUGWORKSPACEMANAGER

turn on the debug mode for the workspace manager (the array routines).

DEGENERATE

Smoothes (slightly) occupation numbers around the Fermi level, so as to insure that nearly-degenerate states get (nearly-) identical occupations. Default=off, but in case of problematic SCF convergence the program will turn this key on automatically, unless the key NODEGENERACY is set in input. The smoothing depends on a parameter EDEGEN, which has a default value of 1e-4 and can be considered a 'degeneration width'. A value different from the default can be supplied as argument to DEGENERATE. A larger value than the default causes smoothing over a larger energy range.

DFLF

All numerical orbitals from the DIRAC subprogram that have angular momentum quantum value up to this value are used (squared) as fit functions for the crystal SCF procedure. Default: -1 (no fit functions from numerical atomic orbitals)

DFRMAX

The DIRAC data (orbitals, potentials, densities) are generated on a radial logarithmic grid, with largest value 100, to be overridden with this key

DFRMIN

The DIRAC data (orbitals, potentials, densities) are generated on a radial logarithmic grid, with smallest value 1e-6, to be overridden with this key

DFRNUC

The DIRAC subprogram takes this as the size for the nucleus. Default 0. Note that only one value can be set, which will apply to all atoms. Therefore, this key is not very useful in its current implementation, unless one uses only one type of atom in the calculation

DFVALENC

requires an integer value argument. It sets whether by default, valence orbitals from the DIRAC subprogram are used as basis functions in the crystal calculation. If this key is absent, or carries the value 0, that default is FALSE, otherwise TRUE.

Note that in the DIRAC data blocks (one for each atom type) one can specify that the valence orbitals are to be included in the crystal basis, overriding then any FALSE default for that. The converse is not possible, i.e. if the default it TRUE, you cannot turn it off for a particular atom type.

DIIS (block-type)

The DIIS procedure to obtain the SCF solution in the crystal depends on several parameters. Default values can be overruled with this key-block. Each option must be specified, it at all, on a separate record in the data block:

DIIS
option1 value1

option2 value2

(etc)
**

Recognized options are:

condition: the condition number of the DIIS matrix, the largest eigenvalue divided by the smallest, must not exceed this value; default 1e6

clarge: when the largest coefficient in the DIIS expansion exceeds this value, damping is applied; default 20

chuge: when the largest DIIS coefficient exceeds this value, the oldest DIIS vector is removed and the procedure re-applied. Default 50

dimix: mixing parameter when damping is used, rather than the DIIS procedure. By default off (dimix=1.0): result is taken as dimix*value + (1-dimix)*previous

nvctrx: maximum number of DIIS expansion vectors. Default 20

ncycledamp: number of initial iterations where damping is applied, before any DIIS is considered. Default 5

valencedensity: (no argument): presence of this string means that the DIIS method will be applied to the valence density, rather than to the potential (potential is the default).

potential: (no argument): presence of this string means that the DIIS method will be applied to the potential. This option is redundant because it represents the default. It excludes the competing options (valencedensity and deformation respectively)

deformationdensity: (no argument): presence of this string means that the DIIS method will be applied to the deformation density, rather than to the potential (default). This option excludes the potential option, see previous.

print: turns on a print switch to report details of the used DIIS procedure. Default off.

special: (no argument) will let the program try to optimize the mixing parameter (dimix) and adjust it when difficulties occur. It is not certain that this may not make things worse!

comstr: its argument is only a string to be printed as label to output, if any, of the DIIS parameter.

DIRIS (block-type)

Completely similar to the DIIS key, except that this one applies to the DIIS procedure used in the DIRAC subprogram, for numerical single atom calculations.

DMADEL

One of the parameters that define the screening of Coulomb-potentials in lattice sums. Depends by default on ACCINT, RMADEL, and RCELX. One should consult the literature for more information

DOTEST

Invokes execution of a subroutine "test", the body of which is to be supplied. The call is executed early, directly after the first initializations. This is a development / debugging tool, not for normal usage.

EIGTHRESHOLD

Components smaller (absolute value) than this parameter (default 1e-2) are not printed in the output of the DOS section, where the breakdown of crystal orbitals in the primitive basis is output.

FERMI (block type) (block type)

This key sets technical parameter used in the search for the Fermi energy, which is carried out at each cycle of the SCF procedure. All applicable options must be specified, if at all, in separate records in the data block:

FERMI

option1 value1

option2 value2

(etc)

**

Recognized options:

maxtry: maximum number of attempts to locate the Fermi energy accurately. Default 50. The procedure is iterative in nature, narrowing the energy band in which the Fermi energy must lie, between an upper and a lower bound. If the procedure has not sufficiently converged within maxtry iterations, the program takes a reasonable value and constructs the charge density by interpolation between the functions corresponding to the last used upper and lower bounds for the Fermi energy

delta: converge criterion: upper and lower bounds for the Fermi energy and the corresponding integrated charge volumes must be equal within delta. Default 1e-4

eps: after convergence of the Fermi energy search procedure, a final estimate is defined by interpolation and the corresponding integrated charge volume is tested. It should be exact, to machine precision. Tested is that it deviates not more than eps. Default 1e-10

FILELENGTH

maximum amount of data (in bytes) on one logical file. Default depends on the machine and should be set at the installation of the program.

FITDEPEND

Criterion for dependency of the total set of fit functions. The value monitored is the smallest eigenvalue of the overlap matrix of normalized bloch sums of symmetrized fit functions. Default=1e-6.

HYBRID

invokes the hybrid quadratic (rather than fully ) quadratic integration method over the BZ. It is meaningful only for 2D Brillouin Zones that would otherwise use a fully quadratic procedure (odd-valued k-space integration parameter ). In all other cases the key is ignored.

INTEGERMEMBLOCK

smallest block of memory to allocate to store integers in (in Megabytes).

INTEGRATION (block-type)

parameter-specifications for the generation of numerical integration points and weights. Most data records must be of the form "parameter value". The most important parameter is ACCINT, which can also be specified separately (i.e. not inside the INTEGRATION-block, but as an independent key). Unless one is very familiar with the details of the numerical integration package, we strongly recommend not to use the INTEGRATION-key, and to specify only ACCINT. More information can be found in the literature.

IOVECTOR

I/O actions to and from files is segmented in blocks of IOVECTOR. Default depends on the machine and should be set at the installation of the program.

IPRNTE

integer print 'level' for eigenstates and -values during the SCF iterations. The higher IPRNTE, the more is printed. Default=0

IPRNTI

integer print level for the numerical integration package. To be used for debugging. Default=1

IPRNTP

integer print level for the general preparation phase of the program. Default=1

IPRNTS

integer print level for the scf procedure in general. Default=0

KGRP0

treatment of the k-points (integration over the Brillouin Zone) in the preparation phase (construction of bloch basis functions, computation of overlap matrix, and so on, in each k-point) is in blocks of KGRP0 points at the same time. Note: last character of this key is a zero (not the letter "o").
During the preparation phase increasing KGRP0 may reduce the CPU time. (This depends also on available workspace). However, larger KGRP0 values result in more files being open at the same time, and more data being stored on disc during this stage of the program. By default the program tries to optimize KGRP0 only with respect to the expected effect on CPU-time.
If the key is used, the actual value of KGRP0 may differ slightly from the input-value: from the input-value the program computes first the number of blocks of k-points; then KGRP0 is re-computed by distributing the total number of k-points equally over the blocks. To restrict the size of the blocks via input it is most convenient to use the key KGRPX, rather than KGRP0.

KGRPX

is an absolute upper bound on KGRP0 as computed by the program.

KMESH

secondary parameter for integration over the Brillouin Zone: some aspects in the quadratic method may be carried out in fact by using a fine-grid linear-tetrahedron method (: hybrid approach). KMESH defines this linear-method mesh. Default=2 (invariably found to be adequate).

LESSDEGENERATESMOOTHING

If smoothing of occupations over nearly degenerate orbitals is applied (see the key DEGENERATE)), then, if this key is set in the input file, the program will limit the smoothing energy range to 1e-4 a.u. as soon as the SCF has converged "halfway", i.e. when the SCF error has decreased to the square root of its convergence criterion.

LinearKspace

Integration over the BZ is carried out with the analytic quadratic tetrahedron method. If the input KSPACE key is set to an even number, this approach is not used and the linear tetrahedron method is used (usually far inferior). To invoke the linear method also for odd values of KSPACE, insert the LINEARKSPACE key (no argument) in the input file.

LNOSPN

Applies only in a spin-unrestricted calculation. The program assumes that energy bands are constituted of the results at the discrete k-points that correspond in energy-ordering: the first band is made up of all lowest eigenvalues across the BZ, the second band of the second lowest values, et cetera. This procedure is, by default, carried out independently for both spins. Using the key "mixes" spin-alpha and spin-beta orbitals and allows spin-mixed bands, so to speak. This affects the calculation of occupation numbers in case of partially filled bands. It is primarily a testing and debugging tool.

LOGICALMEMBLOCK

smallest block of memory to allocate to store logicals in (in Megabytes)

LOWDIN

Applies only in fragments calculations. By default the start-up density is taken as sum-of-fragments. This key specifies that the density is constructed from the fragment orbitals after these have been mutually orthonormalized (Pauli principle). It's only related to SCF convergence considerations. Depending on the system it may or may not improve the required number of SCF cycles.

MIX

Initial 'damping' parameter in the SCF procedure, for the iterative update of the potential: new potential = old potential + mix (computed potential-old potential). Default=0.15.
Note: the program automatically adapts MIX during the SCF iterations, in an attempt to find the optimal mixing value.

NOCOREDISP

By default it is assumed that the core states display some small but non-negligible dispersion. Using this key counteracts this assumption. The core Bloch functions are then computed only in the G-point and assumed to be identical for all k-points in the Brillouin Zone.

NODEGENERACY

This key prevents any internal automatic setting of the key DEGENERATE, see that key's description.

NODIRECTIONALSCREENING

Real space lattice sums of slowly (or non-) convergent terms, such as the Coulomb potential, are computed by a screening technique. In previous releases, the screening was applied to all (long-range) Coulomb expressions. With BAND98 screening is only applied in the periodicity directions. This key restores the original situation: screening in all directions.

NONORTHOGONALSCFBASIS

By default the Bloch sums of elementary one-center basis functions are transformed to an orthonormal basis (by numerical integration). Using this key prevents that; in the SCF procedure diagonalization of the Fock matrix is replaced by a general eigenvalue solver that takes the non-trivial overlap matrix into account.

NUELSTAT

Electrostatic interaction integrals between spherical atomic densities are computed by numerical integration over an elliptic grid. Nuelst is the outward (parabolic) coordinate number of integration points.
Default: 50

NVELSTAT

Electrostatic interaction integrals between spherical atomic densities are computed by numerical integration over an elliptic grid. Nvelst is the angular (elliptic) coordinate number of integration points.
Default: 80

OCCUPATIONS

Allows to input specific occupations numbers. Applies only for calculations that use only one k-point (i.e. pseudo-molecule calculations). The key is block type, the format is, for each line in the block:
irrepno occupations_alpha // occupations_beta
the irrepno must be 1, unless symmetry is used (an unsupported option, currently).
occupations_beta, and the separating double slash (//) must not be used in a spin-restricted calculation.
occupations_alpha/beta is a sequence of values assigned to the states ("bands") in energy ordering.
This allows you, for instance, to specify an empty state below occupied ones.

OLDKPOINTS

The BZ sampling grid is generated in a summation over simplices that build the irreducible wedge of the BZ, considering only the geometric symmetry of the BZ itself. Any additional k-points required, when the atomic positions in the unit cell imply symmetry lowering, are added by symmetry operations. In pre-98 releases of BAND the BZ grid was generated in the symmetry unique part of the BZ considering the real space symmetry (which could, therefore, be a lower symmetry) directly. The difference between the two methods is in particular relevant when doing comparison calculations where the systems differ only in the atomic positions implying different space group symmetries. One would then want to use the same BZ grid. This is the case since release 98, but was not (by default) so in earlier versions. The original approach can be selected by using this key OLDKPOINTS.

PIRPT3

Invokes a slightly different generator for the numerical integration grid. Like the standard method, it is based on an atomic cellular partitioning of space, but it differs in the treatment of the truncated pyramids, by more strictly monitoring test functions. It generates more points (which means: increased CPU times and disk storage), and in some cases it yields more accurate results. General advise is hard to give.

POPTHRESHOLD

Threshold for printing Mulliken population terms. Default 1e-2

POTENTIALNOISE

The initial potential for the SCF procedure is constructed from a sum-of-atoms density. Added to this is some small noise in the numerical values of the potential in the points of the integration grid. The purpose of the noise is to help the program break the initial symmetry, if that would lower the energy, by effectively inducing small differences between (initially) degenerate orbitals. The noise in the potential is randomly generated between zero and an upper limit, which is 1e-4 a.u. by default. The key, which must have a numerical argument, adjusts this upper limit. This can be used therefore to suppress the noise by choosing zero, or to increase it by specifying some large number.

PRINT MEMORY

Print the memory usage as determined by the memchk routine.

PRINT BLCKAT

Print the information about the distance effects used in the numerical integrals.

RCELX

Max. distance of lattice site from which tails of atomic functions will be taken into account for the bloch sums. Default depends on ACCINT.

RHOCHOICE

(With SKIP.) The program knows two alternative ways to evaluate the charge density iteratively in the SCF procedure: from the P-matrix, and directly from the squared occupied eigenstates. By default the program actually uses both at least one time and tries to take the most efficient. SKIP RHOCHOICE turns off this comparison and lets the program stick to one method (from the eigenstates).

RMADEL

One of the parameters that define screening of the Coulomb potentials in lattice summations. Depends by default on ACCINT, DMADEL, RCELX. One should consult for more information

REALMEMBLOCK

Minimum size of the blocks of memory to allocated to store reals in.

SCFLINTHRESH

Criterion for application of approximations in the SCF procedure: the approximate values for the underlying data must be within the criterion (relatively) from the correct ones. Default 1e-10. Typical application: the Hamiltonian matrix, which is CPU intensive to compute, is linearly approximated from previous matrices when the potential, viewed as a vector over the numerical integration grid, is close to a linear combination of previous potential vectors.

SCFRATE

Minimum rate of convergence for the SCF procedure. If progress is too slow the program will take measures (such as smearing out occupations around the Fermi level, see key DEGENERATE) or, if everything seems to fail, it will stop. Default=0.99

SHARP

Suppresses auto-setting DEGENERATE by the program in an attempt to overcome convergence difficulties.

SKIP

followed by any number of strings (separated by blanks or commas) tells the program to skip certain parts. Should only be used by those who know what they're doing. Recognized are certain pre-defined strings. Useful argument may be EIGENVALUES (to suppress printing the eigenvalues at the (first and last) SCF cycles).

STRINGMEMBLOCK

Smallest block of memory to allocate to store strings in (in Megabytes).

SUPPRESS

Suppresses integration in k-space in one or more directions. May be used for instance if the 3D Brillouin Zone is very extended in one or two dimensions and of 'normal' size in the other dimension(s). We plan to remove this key in the future. If it is given in input, with an integer value, integration will be suppressed in the indicated number of dimensions.

TAILCR

One real argument, which should be a small value; default zero. The tail criterion specifies that tails of exponentially decaying (basis, ...) functions are ignored, in the construction of bloch functions, beyond the point where the remaining part of the function tail (radially) integrates to less than the criterion, relative to the integral of the function from zero to infinity. This key must be used together with the key NONORTHOGONALSCFBASIS.

TEMPERATURE

Defines the distribution of occupations around the Fermi level. By default (T=10), the effect is that of zero temperature. In fact this key is a preliminary to a future full implementation of finite temperature effects; currently it has no sensible application. See, however, the ALLBANDS key.

TEST

Changes many default values to lower precision values, so as to run a quick test.

TRAEPS

The real argument (default zero) sets a threshold for setting elements to zero in transformation matrices (typically, for transforming the bloch basis to an orthonormal one, and similar transformations) whenever the absolute value is below the threshold.

VSPLIT

To disturb degeneracy of alpha and beta spin MOs the variable vsplit is added to the beta spin potential at the startup. Default: VSPLIT 5E-2.