Description of the atom type. (For convenience you might prefer to generate them automatically with the BasisDefaults key.) Contains the block keys Dirac, BasisFunctions and FitFunctions. The key corresponds to one atom type. The ordering of the AtomType keys (in case of more than one atom type) is not arbitrary. It is interpreted as corresponding to the ordering of the Atoms keys. The n-th AtomType key supplies information for the numerical atom of the nth type, which in turn has atoms at positions defined by the nth Atoms key.
AtomType Symbol
Dirac ChemSym
{option}
...
shells cores
shell_specification {occupation_number}
...
SubEnd
{BasisFunctions
shell_specification STO_exponent
...
SubEnd}
FitFunctions
shell_specification STO_exponent
...
SubEnd
END
The argument Symbol to AtomType is the symbol that is used in the Atoms key block.
Specification of the numerical ('Herman-Skillman')
free atom,
which defines the initial guess for the SCF density, and which also
(optionally) supplies Numerical Atomic Orbitals (NOs) as basis
functions, and/or as fit functions for the
crystal calculation. The argument ChemSym
of this option is the chemical symbol of the atom type.
The data records of the Dirac key are:
1.the number of atomic shells (1s,2s,2p,etc.) and the nr. of
core-shells (two integers on one line). 2,3
specification of the shell and its electronic occupation.
This specification can be done via quantum numbers or using the
standard designation (e.g. '1 0'
is equivalent to '1s').
Optionally one may insert anywhere in the Dirac
block a record
Valence,
which signifies that all numerical valence orbitals will be used as
basis functions (NOs) in the crystal
calculation.
You can also insert NumericalFit
followed by a number (max. l-value) in the key block, which causes the
program to use numerical fit functions.
For example NumericalFit 2 means that the
squares of all
s,p, and d NOs will be used as fit functions with l=0, since the NOs
are
spherically symmetric.
If you insert Spinor,
a spin-orbit relativistic calculation for the single-atom will be
carried out.
The Herman-Skillman program generates all its functions (atomic potential, charge density, one-electron states) as tables of values in a logarithmic radial grid. The number of points in the grid, and the min. and max. r-value are defaulted at 3000, 0.000001, and 100.0 (a.u.) respectively. These defaults can be overwritten by specifying anywhere in the dirac block the (sub)keys radial, rmin and rmax.
The program will do a spin-unrestricted calculation for the atoms in addition to the restricted one. The occupation of the spin-orbitals will be of maximum spin-multiplicity and cannot be controlled in the Dirac key-block.
Slater-type orbitals, specified by quantum numbers n,l or by the letter designation (e.g. 2p) and one real (alpha) per sto. One sto per record. Use of this key is optional in the sense that Slater-type functions are not needed if other basis functions have been specified (i.e. the numerical atomic orbitals, see key Dirac).
Slater-type fit functions, described in the same way
as in basisfunctions.
Each fitfunctions key corresponds to one
atom type,
the type being the one of the preceding Dirac
key.
The selection choice of a 'good' fit set is a matter of experience.
Fair quality sets are included in the database of the molecular program
ADF.
Example:
AtomType C :: Carbon atom
Dirac C
3 1
VALENCE
1s
2s
2p 2.0
SubEnd
BasisFunctions
1s 1.7
...
SubEnd
FitFunctions
1s 13.5
2s 11.0
...
SubEnd
End
An optional subkey of the AtomType key block is TestFunctions that has the same format as the BasisFunctions and FitFunctions blocks. The TestFunctions block specifies STOs to be used as test functions in the numerical integration package. For the time being the l value is ignored. A possible application is to include a very tight function, to increase the accuracy near a nucleus.
