# ABINIT, internal input variables:

## List and description.

This document lists and provides the description of the name (keywords) of the "internal" variables that are not controlled by the user directly, but are derived from input variables. They are mentioned in the documentation because it is easier to understand the behaviour of some input variables thanks to the explanation of such internal variables. In the database of all input variables, they are prepended with the sign %.

##### Copyright (C) 1998-2017 ABINIT group (DCA,XG,RC,YG,FJ)

### Content of the file : alphabetical list of "internal" variables.

A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K. kptns
L.
M. mband mgfft mgfftdg mpw
N. natpawu ndynimage nelect nfft nfftdg npweps npwsigx npwwfn
O.
P.
Q. qptn
R.
S.
T.
U. usefock usepaw userec
V.
W.
X. xclevel
Y.
Z. ziontypat

kptns
Mnemonics: K-PoinTs re-Normalized and Shifted
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: k-points.
Variable type: real(3,nkpt)
No default

If nqpt=0, or if one is doing a reponse calculation, this internal variable is derived from kpt and kptnrm: kptns(1:3,:)= kpt(1:3,:)/ kptnrm, so that it is kpt renormalized by kptnrm.
If nqpt=1 and one is not doing a ground-state calculation, this internal variable is derived from kpt,kptnrm and qptn kptns(1:3,:)= kpt(1:3,:)/ kptnrm+ qptn(1:3), so that it is kpt renormalized by kptnrm, then shifted by qptn(1:3).

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mband
Mnemonics: Maximum number of BANDs
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: BandOcc.
Variable type: integer
No default

This internal variable derives the maximum number of bands over all k-points and spin-polarisation from nband(1:nkpt*nsppol).

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mgfft
Mnemonics: Maximum of nGFFT
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Planewaves.
Variable type: integer
No default

This internal variable contains the maximum of ngfft(1:3).

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mgfftdg
Mnemonics: Maximum of nGFFT for the Double Grid
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Planewaves.
Variable type: integer
No default

This internal variable contains the maximum of ngfftdg(1:3).

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mpw
Mnemonics: Maximum number of Plane Waves
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Planewaves.
Variable type: integer
No default

This internal variable gives the maximum of the number of plane waves over all k-points. It is computed from ecut and the description of the cell, provided by acell, rprim, and/or angdeg.

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natpawu
Mnemonics: Number of AToms on which PAW+U is applied
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: DFT+U.
Variable type: integer
No default
Only relevant if usepawu==1

This internal variable gives the number of atoms on which the LDA/GGA+U method is applied. This value is determined from lpawu.

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ndynimage
Mnemonics: Number of DYNamical IMAGEs
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: PIMD.
Variable type: integer
No default

This internal variable gives the number of dynamical images, immediately deduced from the number of non-zero values present in dynimage. It is used to dimension many memory-consuming arrays (one copy for each image), e.g. the wavefunction array (cg), the density array (rho), etc .

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nelect
Mnemonics: Number of ELECTrons
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: BandOcc.
Variable type: real
Default is AUTO_FROM_PSP

This internal variable gives the number of electrons per unit cell, as computed from the sum of the valence electrons related to each atom (given in the pseudopotential, where it is called "zion"), and the input variable charge:
nelect=zion-charge.

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nfft
Mnemonics: Number of FFT points
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Planewaves.
Variable type: integer
No default

If space parallelisation is not used (that is, if paral_kgb==0), this internal variable gives the number of Fast Fourier Transform points in the grid generated by ngfft(1:3). It is simply the product of the three components of ngfft.
If space parallelisation is used (that is, if paral_kgb==1), then it becomes the number of Fast Fourier Transform points attributed to the particular processor. It is no longer the above-mentioned simple product, but a number usually close to this product divided by the number of processors on which the space is shared.

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nfftdg
Mnemonics: Number of FFT points for the Double Grid
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Planewaves.
Variable type: integer
No default

If space parallelisation is not used (that is, if paral_kgb==0), this internal variable gives the number of Fast Fourier Transform points in the (double) grid generated by ngfftdg(1:3). It is simply the product of the three components of ngfftdg.
If space parallelisation is used (that is, if paral_kgb==1), then it becomes the number of Fast Fourier Transform points attributed to the particular processor. It is no longer the above-mentioned simple product, but a number usually close to this product divided by the number of processors on which the space is shared.

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npweps
Mnemonics: Number of PlaneWaves for EPSilon (the dielectric matrix)
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Susceptibility.
Variable type: integer
No default

npweps determines the size of the planewave set used to represent the independent-particle susceptibility $\chi^{(0)}_{KS}$, the dielectric matrix $\epsilon$ and its inverse.
It is an internal variable, determined from ecuteps.

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npwsigx
Mnemonics: Number of PlaneWaves for SIGma eXchange
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: SelfEnergy.
Variable type: integer
No default

npwsigx determines the cut-off energy of the planewave set used to generate the exchange part of the self-energy operator.
It is an internal variable, determed from ecutsigx.

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npwwfn
Mnemonics: Number of PlaneWaves for WaveFunctioNs
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topics: Susceptibility, SelfEnergy.
Variable type: integer
No default

npwwfn is the size of the planewave set used to represent the wavefunctions in the formula that generates the independent-particle susceptibility $\chi^{(0)}_{KS}$. It is an internal variable, determined from ecutwfn.

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qptn
Mnemonics: Q-PoinT re-Normalized
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: DFPT.
Variable type: real(3)
Default is 3*0
Only relevant if nqpt==1

Only used if nqpt=1.
In ground-state calculation, the vector qptn(1:3) is added to each renormalized k point (whatever the value of kptopt that was used) to generate the normalized, shifted, set of k-points kptns(1:3,1: nkpt ).
In response-function calculations, qptn(1:3) is the wavevector of the phonon-type calculation.
qptn(1:3) can be produced on the basis of the different methods described in qptopt, like using qpt(1:3) with renormalisation provided by qptnrm, or using the other possibilities defined by iqpt, ngqpt, nshiftq, qptrlatt, shiftq,
For insulators, there is no restriction on the q-points to be used for the perturbations. By contrast, for metals, for the time being, it is advised to take q points for which the k and k+q grids are the same (when the periodicity in reciprocal space is taken into account). Tests remain to be done to see whether other q points might be allowed (perhaps with some modification of the code).

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usefock
Mnemonics: USE FOCK exact exchange
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Hybrids.
Variable type: integer
Default is 0

This internal variable is automatically set to 1 when the value of ixc refers to an Hartree-Fock calculation or hybrid functionals.

- 0 => No use of exact exchange.
- 1 => exact exchange is required for the calculation.

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usepaw
Mnemonics: USE Projector Augmented Waves method
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: PAW.
Variable type: integer
Default is AUTO_FROM_PSP

This variable is determined by the pseudopotentials files. PAW calculations (see paw1) can only be performed with PAW atomic data input files, while pseudopotential calculations are performed in ABINIT with norm-conserving pseudopotential input files. Most functionalities in ABINIT are available with either type of calculation.

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userec
Mnemonics: USE RECursion
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topic: Recursion.
Variable type: integer
Default is 0

This internal variable is set to 1 when the recursion method is activated (see tfkinfunc).

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xclevel
Mnemonics: eXchange Correlation functional LEVEL
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topics: xc, TDDFT.
Variable type: integer
Default is 0

Automatically determined from the value of ixc.

- 0 => No XC contribution.
- 1 => LDA functional.
- 2 => GGA functional or hybrid functional based on GGA.
- 3 => Functional for TDDFT.

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ziontypat
Mnemonics: Z (charge) of the IONs for the different TYPes of AToms
Executable: abinit
Characteristic: INTERNAL_ONLY
Mentioned in topics: AtomTypes, PseudosPAW.
Variable type: real(ntypat)
Default is AUTO_FROM_PSP

Charge of the pseudo-ion (=number of valence electrons that are needed to screen exactly the pseudopotential).

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