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tips for PP generation
Date: 2007/02/07 00:19
Name: Denis Music   <music@mch.rwth-aachen.de>

Dear OpenMX users,
I've started to use the code and so far I've done some basic tests. E.g. the bulk modulus of diamond turned out to be just fine. A more demanding job is to have a reasonable data on transition metal carbides, nitrides, and oxides. So I started with TiC and VO, both having NaCl structure, and I used the available PP. However, their bulk moduli (lattice parameters as well) are far from the experimental values. Since I'm not experienced with the ADPACK code and PP generation in general, I’d really appreciate some hints. Does, for instance, optimization of already available PP help?
With best regards,
Denis
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Re: tips for PP generation ( No.1 )
Date: 2007/02/07 18:16
Name: Denis Music  <music@mch.rwth-aachen.de>

Dear Prof. Ozaki and OpenMX users,

I've been trying to calculate bulk moduli of transition metal carbides and oxides and have run into serious problems. Just to test the code, I did a run with diamond (LDA), which gave the following E-V data:

V(Bohr3) E(Hartree)
55.282344239957 -11.710087565044
66.309120422585 -11.766139016881
72.333694741460 -11.776363197750
76.117849485348 -11.776638592378
78.712556544783 -11.775442650191
92.573632602995 -11.755242652100
107.973328593666 -11.717515494710

Using B-M EOS, the bulk modulus was 446 GPa, which is expected.
Then, I tried with VO (NaCl structure) with both LDA and GGA (downloaded from this website). The input file was as follows:

System.CurrrentDirectory ./ # default=./
System.Name vo
level.of.stdout 1 # default=1 (1-3)
level.of.fileout 1 # default=1 (1-3)
Species.Number 2
<Definition.of.Atomic.Species
V V4.0 V_PBE
O O4.5-s2p2 O_GGA
Definition.of.Atomic.Species>
Atoms.Number 2
atoms.SpeciesAndCoordinates.Unit FRAC
<Atoms.SpeciesAndCoordinates
1 V 0.000 0.000 0.000 6.5 6.5
2 O 0.500 0.500 0.500 3.0 3.0
Atoms.SpeciesAndCoordinates>
Atoms.UnitVectors.Unit Ang # Ang|AU
<Atoms.UnitVectors
1.4500 1.4500 0.0000
1.4500 0.0000 1.4500
0.0000 1.4500 1.4500
Atoms.UnitVectors>
scf.XcType GGA-PBE # LDA|LSDA
scf.SpinPolarization off # On|Off
scf.ElectronicTemperature 300.0 # default=300 (K)
scf.energycutoff 250.0 # default=150 (Ry)
scf.maxIter 300 # default=40
scf.EigenvalueSolver band # Recursion|Cluster|Band
scf.Kgrid 7 7 7 # means 4x4x4
scf.Mixing.Type rmm-diisk # Simple|Rmm-Diis|Gr-Pulay
scf.Init.Mixing.Weight 0.30 # default=0.30
scf.Min.Mixing.Weight 0.001 # default=0.001
scf.Max.Mixing.Weight 0.700 # default=0.40
scf.Mixing.History 7 # default=5
scf.Mixing.StartPulay 5 # default=6
scf.criterion 1.0e-10 # default=1.0e-6 (Hartree)
scf.lapack.dste dstevx # dstegr|dstedc|dstevx, default=dstegr
1DFFT.NumGridK 900 # default=900
1DFFT.NumGridR 900 # default=900
1DFFT.EnergyCutoff 3600.0 # default=3DFFT.EnergyCutoff*3.0 (Ry)
orbitalOpt.Method Off # Off|Unrestricted|Restricted
orbitalOpt.InitCoes Symmetrical # Symmetrical|Free
orbitalOpt.initPrefactor 0.1 # default=0.1
orbitalOpt.scf.maxIter 12 # default=12
orbitalOpt.MD.maxIter 2 # default=5
orbitalOpt.per.MDIter 2 # default=1000000
orbitalOpt.criterion 1.0e-4 # default=1.0e-4 (Hartree/borh)^2
CntOrb.fileout off # on|off , default=off
Num.CntOrb.Atoms 2 # default=1
<Atoms.Cont.Orbitals
1
2
Atoms.Cont.Orbitals>
orderN.HoppingRanges 4.0 # default=5.0 (Ang)
orderN.NumHoppings 1 # default=2
MD.Type nomd # Nomd|Constant_Energy_MD|Opt
MD.maxIter 1 # default=1
MD.TimeStep 1 # default=0.5 (fs)
MD.Opt.criterion 1.0e-5 # default=1.0e-4 (Hartree/bohr)
MO.fileout off # on|off
num.HOMOs 1 # default=1
num.LUMOs 1 # default=1
MO.Nkpoint 1 # default=1
<MO.kpoint
0.0 0.0 0.0
MO.kpoint>
Dos.fileout off # on|off , default=off
Dos.Erange -10.0 10.0 # default = -20 20
Dos.Kgrid 9 9 9 # default = Kgrid1 Kgrid2 Kgrid3
HS.fileout off # on|off, default=off

This gave the following E-V data:

V(Bohr3) E(Hartree)
41.146273610483 -60.434642363040
45.551248000453 -62.542659087940
50.259897377092 -63.349043408228
55.282344239957 -63.257714865316
60.628711088603 -62.561496909954
66.309120422585 -61.750487048134

However, the equilibrium volume is 50% of the expected one and of course this gave unphysical bulk modulus.

I'd really appreciate your help. Am I doing something wrong with the input file? I have hard time believing that any PP can give this large overbinding (factor 2).

With best regards,
Denis
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Re: tips for PP generation ( No.2 )
Date: 2007/02/07 19:44
Name: T.Ozaki

Hi,

"V V4.0 V_PBE" means that no basis function is assigned for vanadium.
For vanadium, a possible choice is V5.5-s2p2d1, while a careful check
is required.

Regards,

TO
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Re: tips for PP generation ( No.3 )
Date: 2007/02/08 00:20
Name: Denis Music  <music@mch.rwth-aachen.de>

Dear Prof. Ozaki,
Thanks a lot for your tip. I've tried to rerun the whole calculation and everything seems fine now. I also did a comparison with VASP and EMTO and the agreement is quite OK.
With best regards,
Denis
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