mirror of https://github.com/abinit/abinit.git
125 lines
5.3 KiB
Markdown
125 lines
5.3 KiB
Markdown
## Information on the format 6 for pseudopotentials
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The format 6 for ABINIT pseudopotentials allows to use pseudopotentials
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generated from the FHI98PP code (Fritz-Haber-Institute, Berlin).
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This code is available at this [URL](http://www.FHI-Berlin.MPG.DE/th/fhi98md/fhi98PP).
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A few lines must be added to the file generated by the FHI98PP code,
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and are described in the present file. ABINITv1.9 is able to
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read format 6 pseudopotential files without core correction.
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ABINITv2.2 is able to read them with core correction (thanks to AF).
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# The original cpi file
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We will suppose that the user has been able to generate a `cpi` file from the FHI98PP code.
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There is one such file in the `~abinit/tests/Pspdir` directory,
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with the name `al_h.cpi` (the FHI98PP code generated a file named `al:h.cpi`,
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but the name was changed, to allow portability under DOS/Windows) .
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It begins by:
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0.30000000000000E+01 3
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0.0000 0.0000 0.0000 0.0000
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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0.0000 .00e+00 .00e+00
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493 0.10247000000000E+01
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1 0.48076923076923E-03 0.91926957204792E-04 0.72762392428392E+00
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2 0.49264423076923E-03 0.94197553047751E-04 0.72762434262851E+00
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3 0.50481254326923E-03 0.96524232608030E-04 0.72762477651319E+00
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...
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...
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From these numbers, we will make direct use of:
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- those on the first line, i.e. the number of valence electrons ( 0.30000000000000E+01 )
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and the number of pseudopotential components ( 3 )
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- the first on the 12th line, i.e. the number of mesh points ( 493 )
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# The new file
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For the purpose of generating the corresponding file readable by ABINIT (also
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found in the `~abinit/tests/Pspdir` directory, with the name `13al.981214.fhi`),
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the following seven lines have been added at the beginning of the `al_h.cpi file`:
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Aluminum, fhi98PP : Hamann-type, LDA CA PerdewWang, l=2 local
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13.000 3.000 981214 zatom,zion,pspdat
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6 7 2 2 493 0 pspcod,pspxc,lmax,lloc,mmax,r2well
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0.0 0.0 0.0 rchrg, fchrg, qchrg
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5--- These two lines are available for giving more information, later
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6
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7-Here follows the cpi file from the fhi98pp code-
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Similar lines must be added at the beginning of other cpi files, in order
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to make them readable by ABINIT.
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Line 1 is simply a header, that might include any information, and that will
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be printed without modification in the output of ABINIT.
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Line 2 describes:
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- the atomic number (zatom);
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- the ionic charge (zion, number of valence electrons);
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- the date of pseudopotential generation.
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The two first information are crucial, the third one is not
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really important. The atomic number is 1 for Hydrogen, 8 for Oxygen, and so on.
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The ionic charge should be the same number as the first number mentioned
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in the cpi file (called 'number of valence electrons').
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Line 3 describes:
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- the format of the pseudopotential (pspcod; must be 6 for this format);
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- the XC functional used to generate the pseudopotential (pspxc ; the
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same numbers as for the input variable ixc should be used,
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see `~abinit/doc/users/abinit_help.html`)
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- the maximal angular momentum of the wavefunctions described
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in the pseudopotential file (lmax=0 if only s-wavefunctions are present,
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lmax=1 for s and p wfs, lmax=2 for s, p and d wfs ... ; lmax+1 must be
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equal to the 'number of pseudopotential components' mentioned in the cpi
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file, as the second number of the first line)
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- the angular momentum of the potential to be used as local pseudopotential
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(lloc=0 if s-potential is local; lloc=1 if p-potential is local ; ... )
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- the number of radial mesh points (mmax, same meaning as in the cpi file;
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first number on the 12th line)
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- the last number can be set to 0 .
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Line 4 describes 3 parameters needed to read the model core-charge
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if core correction is needed.
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- rchrg: radius at which the core charge vanish (i.e. cut-off in a.u.)
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- fchrg: amplitude of core charge (if =0 non core-correction performed,
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if >0 core-correction is applied). The specific value of fchrg
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has no physical meaning in fhi98pp scheme of core correction.
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- qchrg: integrated model core charge (it's not actually used by
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abinit, and can be set to any value)
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rchrg can be inferred by the pp file. Indeed, if the pp has been generated
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with the core-correction option, at the end of 'cpi' file there will be:
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do i=1,mmax
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rad(i), f(i), f1(i), f2(i)
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end do
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that is, the radial grid, the core charge (f), and their first(f1)
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and second (f2) derivative on the radial mesh; rchrg can be equal
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to any value of rad(i) to which f,f1 and f2 are reasonably vanished.
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Line 5-7 have no interest up to now.
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A pseudopotential with format 6 will be treated by
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the routine `psp6in.f`, that calls `psp5lo.f` (local part) and `psp5nl.f` (non-local part).
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There is no `psp6lo.f` or `psp6nl.f`.
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The integral of (V(r)+Zion/r) r^2 in psp5lo.f is performed
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from 0 to the highest allowed radius (usually about 100 a.u.),
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except that beyond 20 a.u. no value of abs(V(r)) larger than 2.0d-8 is tolerated.
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This will allow to cut off spurious behaviour of pseudopotential whose data file
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is written in single precision.
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