ABINIT, PAW input variables:

List and description.


This document lists and provides the description of the name (keywords) of the input variables for runs based on the Projector Augmented Waves methodology, to be used in the main input file of the abinis code.

The new user is advised to read first the new user's guide, before reading the present file. It will be easier to discover the present file with the help of the tutorial.

When the user is sufficiently familiarized with ABINIT, the reading of the ~abinit/doc/users/tuning file might be useful. For response-function calculations using abinis, please read the response function help file

Copyright (C) 1998-2007 ABINIT group (DCA, XG, RC)
This file is distributed under the terms of the GNU General Public License, see ~abinit/COPYING or http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

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Files that describe other input variables:

Content of the file : alphabetical list of PAW input variables.


A.
B. bxctmindg  
C.
D. dmatpawu  
E.
F.
G.
H.
I. iboxcut  
J. jpawu  
K.
L. lpawu  
M. mqgriddg  
N. ngfftdg  
O.
P. pawecutdg   pawlcutd   pawlmix   pawmixdg   pawnphi   pawntheta   pawnzlm   pawoptmix   pawovlp   pawprtdos   pawprtvol   pawsphmix   pawstgylm   pawxcdev   prtefg   prtnabla  
Q. quadmom  
R.
S.
T.
U. usedmatpu   upawu   usepawu  
V.
W.
X.
Y.
Z.




bxctmindg
Mnemonics: BoX CuT-off MINimum for the Double Grid (PAW)
Characteristic:
Variable type: real parameter
Default is 2.0

Relevant only when usepaw=1.
The box cut-off ratio is the ratio between the wavefunction plane wave sphere radius, and the radius of the sphere that can be inserted in the FFT box, in reciprocal space.
If the density were only generated from wavefunctions, in order for the density to be exact, this ratio should be near two. If one uses a smaller ratio, one will gain speed, at the expense of accuracy. In case of pure ground state calculation (e.g. for the determination of geometries), this is sensible. However, the wavefunctions that are obtained CANNOT be used for starting response function calculation.
However, some augmentation charge is always added in PAW, and even with the box cut-off ratio larger than two, the density is never exact. Sometimes, this ratio must be much larger than two for the computation to be converged at the required level of accuracy.




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dmatpawu
Mnemonics: initial Density MATrix for PAW+U
Characteristic:
Variable type: real array dmatpawu(2*max(lpawu)+1, 2*max(lpawu)+1, nsppol, %natpawu)
where %natpawu is the number of atoms on which LDA/GGA+U is applied.

default is -10. (not defined) 

Relevant only when usepaw=1, usepawu=1, and usedmatpu>0.
Gives the value of an initial density matrix used in LDA+U and kept fixed during the first usedmatpu SCF iterations.
Only components corresponding to lpawu angular momentum are requested.
Restriction: lpawu must be identical for all atom types (or -1).




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iboxcut
Mnemonics:
Characteristic:
Variable type: integer parameter
Default is 0

Concern all summations in the reciprocal space and is allowed in PAW and norm-conserving.
  • if set to 0 all reciprocal space summations are done in a sphere contained in the FFT box.
  • if set to 1 all reciprocal space summations are done in the whole FFT box (usefull for tests).




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jpawu
Mnemonics: value of J for PAW+U
Characteristic: ENERGY
Variable type: real array jpawu(
ntypat)
default is 0

Relevant only when usepaw=1, and usepawu=1.

Gives the value of the screened exchange interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.




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lpawu
Mnemonics: value of angular momentum L for PAW+U
Characteristic:
Variable type: integer array lpawu(ntypat)
Default is -1

Activated if usepawu is equal to 1 or 2.
Give for each species
the value of the angular momentum (only values 2 or 3 are allowed)  on which to apply the LDA+U correction.
  • If equal to 2 (d-orbitals)  or 3 (f-orbitals), values of upawu and  jpawu are used in the calculation.
  • If equal to -1: do not apply LDA+U correction on the species.




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mqgriddg
Mnemonics:
Characteristic: DEVELOP
Variable type: integer parameter
Default is 3001

Maximum number of wavevectors used to sample the local part of the potential, in PAW. Actually referred to as mqgrid_vl internally. Should change name to the latter ... See also mqgrid



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ngfftdg
Mnemonics: Number of Grid points for Fast Fourier Transform : Double Grid
Characteristic:
Variable type: integer array ngfftdg(3)
Default is 0 0 0 (so, automatic selection of optimal values)

Relevant only when usepaw=1.
This variable has the same meaning as ngfft (gives the size of fast Fourier transform (fft) grid in three dimensions) but concerns the "double grid" only used for PAW calculations.




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pawecutdg
Mnemonics: PAW - Energy CUToff for the Double Grid
Characteristic: ENERGY
Variable type: real parameter
Default is -1, so pawecutdg MUST be specified for PAW calculations.

Needed only when usepaw=1.
Define the energy cut-off for the fine FFT grid (the "double grid", that allows to transfer data from the normal, coarse, FFT grid to the spherical grid around each atom).
pawecutdg must be larger or equal to ecut. If it is equal to it, then no fine grid is used. The results are not very accurate, but the computations proceed quite fast.
For typical PAW computations, where ecut is on the order of 15 Ha, pawecutdg should be on the order of 40 Ha. Choosing a larger value should not increase the accuracy, but does not slow down the computation either, only the memory. The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.




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pawlcutd
Mnemonics: PAW - 1+L angular momentum used to CUT the development in moments of the Densitites
Characteristic:
Variable type: integer parameter
Default is 10

Relevant only when usepaw=1.
The expansion of the densities in angular momenta is performed up to l=pawlcutd-1.
The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.




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pawlmix
Mnemonics: PAW - maximum L used in the spherical part MIXing
Characteristic:
Variable type: integer parameter
Default is 10

Relevant only when usepaw=1.
The choice made for this variable determine how the spherical part of the density is mixed during electronic iterations.

Only parts of augmentation occupancies (rhoij quantities) associated with l angular momenta up to l=pawlmix are mixed. Other parts of augmentation occupancies are not included in the mixing process.
This option is usefull to save CPU time but DOES have a bearing on the numerical accuracy of the results.




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pawmixdg
Mnemonics: PAW - MIXing is done (or not) on the (fine) Double Grid
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1.
The choice made for this variable determine on which grid the density (or potential) is mixed during the SCF cycle.

- If pawmixdg=1 the density/potential is mixed in REAL space using the fine FFT grid (defined by pawecutdg or ngfftdg).
- If pawmixdg=0 the density/potential is mixed in RECIPROCAL space using the coarse FFT grid (defined by ecut or ngfft). Only components of the coarse grid are mixed using the scheme defined by iscf; other components are only precondionned by diemix and simply mixed.
This option is useful to save memory and does not affect numerical accuracy of converged results. If pawmixdg=1, density and corresponding residual are stored for previous iterations and are REAL arrays of size nfftdg. If pawmixdg=0, density and corresponding residual are stored for previous iterations and are COMPLEX arrays of size nfft. The memory saving is particulary efficient when using the Pulay mixing (iscf=7 or 17).




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pawnphi
Mnemonics: PAW - Number of PHI angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer parameter
Default is 13

Needed only when usepaw=1.
Number of phi angles (longitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawnphi and pawntheta.




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pawntheta
Mnemonics: PAW - Number of THETA angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer parameter
Default is 12

Relevant only when usepaw=1.
Number of theta angles (latitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawntheta and pawnphi.




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pawnzlm
Mnemonics: PAW - only compute Non-Zero LM-moments of spherical density
Characteristic:
Variable type: integer parameter
Default is 1

Relevant only when usepaw=1.
Concerns the computation of the spherical density (named rho_1 - rho_tild_1).
If set to 0, all lm-moments of the spherical density are computed at each electronic iteration br> If set to 1, only non-zero lm-moments of the spherical density are computed at each electronic iteration (they are all computed at first iteration then only the non-zero ; thus the first iteration is more cpu expensive)




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pawoptmix
Mnemonics: PAW - OPTion for the MIXing of the spherical part
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1.
When PAW is activated, the self-consistent requires the mixing of both the total potential (or density) and the "spherical part" (in fact the augmentation occupancies rho_ij).
The same mixing scheme is applied to the potential (density) and the spherical part. It is optimized in order to minimize a residual.
If pawoptmix=0 the residual is the potential (or density) residual.
If pawoptmix=1 the residual is a sum of the potential (or density) residual and the "spherical part" residual.




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pawovlp
Mnemonics: PAW - spheres OVerLap allowed (in percentage)
Characteristic:
Variable type: real parameter
Default is 5.0

Relevant only when usepaw=1.
When PAW is activated, a localized atomic basis is added to describe wave functions. Spheres around atoms are defined and they are IN THEORY not allowed to overlap. However, a little overlap can be allowed without compromising accurary of results. Be aware that too high overlaps can lead to unphysical results.
With the pawovlp variable, the user can control the (voluminal) overlap percentage allowed without stopping the execution.
pawovlp is the value (in percentage: 0...100%) obtained by dividing the volume of the overlap of two spheres by the volume of the smallest sphere.
The following values are permitted for pawovlp:
- pawovlp<0. : overlap is always allowed
- pawovlp=0. : no overlap is allowed
- pawovlp>0. and <100. : overlap is allowed only if it is less than pawovlp %




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pawprtdos
Mnemonics: PAW: PRinT partial DOS contributions
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1 and prtdos=3.
Control print of all the contributions to the PAW partial DOS in _DOS file(s):
- Plane-waves contribution
- "on-site" contribution (phi)
- "on-site" pseudo contribution (phi_tild).
Note that when pawprtdos=1 integrated DOS is not output.




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pawprtvol
Mnemonics: PAW: PRinT VOLume
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1.
Control print volume and debugging output for PAW. If set to 0, the print volume is at its minimum. pawprtvol can have values from 0 to 3.



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pawsphmix
Mnemonics: PAW - SPHerical part MIXing factor
Characteristic:
Variable type: real parameter
Default is equal to diemix

Relevant only when usepaw=1.
pawsphmix is the factor used when preconditionning the spherical part residual (the rhoij residual, where rhoij are the augmentation occupancies)




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pawstgylm
Mnemonics: PAW - option for the STorage of G_l(r).YLM(r)
Characteristic:
Variable type: integer parameter
Default is 1

Relevant only when usepaw=1.
When PAW is activated, the computation of compensation charge density (so called "hat" density) requires the computation of g_l(r).Y_lm(r) factors (and cartesian derivatives) at each point of real space contained in PAW spheres. The number of atoms, of (l,m) quantum numbers and the sharpness of the real FFT grid can lead to a very big {g_l.Y_lm} datastructure. One can save memory by putting pawstgylm=0; but, in that case, g_l(r).Y_lm(r) factors a re-computed each time they are needed and CPU time increases.

Possible choices:
- pawstgylm=0 : g_l(r).Y_lm(r) are not stored in memory and recomputed.
- pawstgylm=1 : g_l(r).Y_lm(r) are stored in memory.

Note:
g_l(r) are shape functions (analytically known)
Y_lm(r) are real spherical harmonics




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pawxcdev
Mnemonics: PAW - choice for eXchange-Correlation DEVelopment (spherical part)
Characteristic:
Variable type: integer parameter
Default is 1

Relevant only when usepaw=1.
  • If set to 0, the exchange-correlation term in the spherical part of energy is totally computed on the angular mesh
  • If set to 1, the exchange-correlation term in the spherical part of energy is developped onto lm-moments at order 1
  • If set to 2, the exchange-correlation term in the spherical part of energy is developped onto lm-moments at order 2 (can be memory/CPU consuming)

Be careful: GGA requires pawxcdev > 0




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prtefg
Mnemonics: PRint Electric Field Gradient
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1.
  • If set to 1, calculate the electric field gradient at each atomic site in the unit cell. Values written to main output file (search for Electric Field Gradient). If prtefg=1, only the quadrupole moment coupling in MHz and asymmetry are given. If prtefg=2, the full tensors in atomic units are also given, showing separate contributions from the valence electrons, the ion cores, and the PAW reconstruction.




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prtnabla
Mnemonics: PRint NABLA
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when usepaw=1.
  • If set to 1, calculate the matrix elements <Psi_n|-inabla|Psi_m> and write it in file _OPT to be read by the code conducti.




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quadmom
Mnemonics: QUADrupole MOMents
Characteristic:
Variable type: real array quadmom(
ntypat)
default is 0

Relevant only when usepaw=1, and prtefg = 1 or greater.
  • Array of quadrupole moments, in barns, of the nuclei.




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upawu
Mnemonics: value of U for PAW+U
Characteristic: ENERGY
Variable type: real array upawu
(ntypat)
default is 0 

Relevant only when usepaw=1, and usepawu=1.
Gives the value of the screened coulomb interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.




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usedmatpu
Mnemonics: USE of an initial Density MATrix in Paw+U
Characteristic:
Variable type: integer parameter
default is 0 

Relevant only when usepaw=1, and usepawu=1.
When usedmatpu/=0, an initial density matrix (given by dmatpawu keyword) is used and kept fixed during the first usedmatpu SCF steps.
This starting value of the density matrix can be useful to find the correct ground state; Within LDA+U formalism, finding the minimal energy of the system is tricky; thus it is adviced to test several values of the initial density matrix.
Note also that the density matrix has to respect some symmetry rules according to the space group.




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usepawu
Mnemonics:  USE PAW+U (spherical part)
Characteristic:
Variable type: integer parameter
Default is 0

Relevant only when  usepaw=1.
  • If set to 0, the LDA+U method is not used.
  • If set to 1, the LDA+U method is used with the Full Localized Limit (FLL) (or Atomic limit) double counting  (A. Lichtenstein et al PRB 52, 5467 (1995))
  • If set to 2, the LDA+U method is used with the Around Mean Field (AMF) double counting (M. T. Czyzyk and G. A. Sawatzky PRB 49, 14211 (1994))
If LDA+U is activated (usepawu=1 or 2), the lpawu, upawu and  jpawu  input variables are read.
The implementation is done inside spheres only

Suggested acknowledgment:
   - B. Amadon, F. Jollet and M. Torrent (in preparation).

(See also   Bengone et al PRB 62, 16392 (2000)).




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