The atoms assembled in a molecule or a solid are physically specified by their nuclear charge (and their mass for dynamical properties).
However, in a pseudopotential
or PAW approach, the knowledge of the nuclear charge does not define the potential felt by the electron,
only the atomic data file (pseudopotential or PAW) defines it. Thus, in addition to the number of types
of atoms ntypat, and their nuclear charge znucl,
ABINIT requires to know the pseudopotential/PAW to use for each type of atom.
The latters are specified in the "files" file. Unless alchemical potentials are used (see later),
the number of pseudopotentials to be read, npsp, is the same as ntypat.
Note that one cannot mix norm-conserving pseudopotentials with PAW atomic data files in a single ABINIT run,
even for different datasets. One has to stick either to norm-conserving pseudopotentials or to PAW.
More on the pseudos/PAW in PseudosPAW.
ABINIT also has a default table of the atomic masses, but this can be superceded by specifying amu.
Alchemical potentials
For norm-conserving pseudopotentials, ABINIT can mix the pseudopotentials, as described in the ABINIT wiki, to create so-called "alchemical potentials", see mixalch.Compulsory input variables:
... ntypat [Number of TYPes of AToms]
... znucl [charge -Z- of the NUCLeus]
Basic input variables:
... amu [Atomic Mass Units]
... typat [TYPe of AToms]
Useful input variables:
... mixalch [MIXing coefficients for ALCHemical potentials]
... npsp [Number of PSeudoPotentials]
... ntypalch [Number of TYPe of atoms that are "ALCHemical"]
Relevant internal variables:
... %npspalch [Number of PSeudoPotentials that are "ALCHemical"]
... %ntyppure [Number of TYPe of atoms that are "PURe"]
... %ziontypat [Z (charge) of the IONs for the different TYPes of AToms]
Input variables for experts:
... algalch [ALGorithm for generating ALCHemical pseudopotentials]
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tests/v3/Input: t92.in t93.in t94.in t95.in t96.in t97.in
tests/v5/Input: t44.in
tests/v6/Input: t28.in
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