This page gives hints on how to specify the types of atoms that form the system.
ABINIT needs to know the different types of atoms that form the system. 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 topic_PseudosPAW.
ABINIT also has a default table of the atomic masses, but this can be superceded by specifying amu.
For norm-conserving pseudopotentials, ABINIT can mix the pseudopotentials, as
described in the ABINIT wiki,
to create so-called “alchemical potentials”, see mixalch.
In this case, the number of pseudopotentials to be given, npsp, will usually be larger than the number of types of atoms, ntypat. Using alchemical potentials makes sense to treat alloys in which similar ions are present, and whose specific chemical properties are not crucial for the property of interest. Usually it is done only for isovalent species, and ions of quite similar radii. It is a reasonable interpolation technique for the electronic properties.
Related Input Variables¶
- mixalch MIXing coefficients for ALCHemical potentials
- npsp Number of PSeudoPotentials to be read
- ntypalch Number of TYPe of atoms that are “ALCHemical”
- algalch ALGorithm for generating ALCHemical pseudopotentials
- %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
Selected Input Files¶
- Tutorial on polarization and finite electric fields. Polarization, and responses to finite electric fields for AlAs. In the present topic, it is an example of the definition of several atom types …