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Binding energy calculation
Date: 2006/10/12 03:08
Name: K. Bart   <kk.bart@gmail.com>

Dear Professor Ozaki,

I am not a specialist in this field, so excuse me if this is a trivial question.

I calculated the binding energy of the W-O dimer (Tungsten Oxide) as a function of
interatomic distance. I set the calculations and got results, but the resulting curve seems to be scattered. I also calculated the O-O dimer in the analogous way, to test my calculations, and got a minimum energy at a distance 1.4 angstrom instead of the literature value of 1.2.

I would be very grateful if you could point me what am I doing wrong and suggest how to set these calculations in the appropriate way to get precise results. For tungsten, I used W11.0 and W_PBE VPS from your database (2006) and took s2p1d1f1. Below you can find my input file.

Best Regards
K. Bart



====================================================================
System.CurrrentDirectory ./ # default=./
System.Name WO
level.of.stdout 1 # default=1 (1-3)
level.of.fileout 1 # default=1 (1-3)

#
# Definition of Atomic Species
#

Species.Number 2
<Definition.of.Atomic.Species
W W11.0-s2p1d1f1 W_PBE
O O6.0--s1p1 O_GGA
Definition.of.Atomic.Species>

#
# Atoms
#

Atoms.Number 2
Atoms.SpeciesAndCoordinates.Unit Ang # Ang|AU
<Atoms.SpeciesAndCoordinates
1 W 0.000 0.000 0.000 12.0 16.0
2 O 0.000 0.000 1.900 4.0 2.0
Atoms.SpeciesAndCoordinates>
Atoms.UnitVectors.Unit Ang # Ang|AU

<Atoms.UnitVectors
12.0000 0.0000 0.0000
0.0000 12.0000 0.0000
0.0000 0.0000 12.0000
Atoms.UnitVectors>

#
# SCF or Electronic System
#

scf.XcType GGA-PBE # LDA|LSDA-CA|LSDA-PW
scf.SpinPolarization on # On|Off
scf.ElectronicTemperature 600.0 # default=300 (K)
scf.energycutoff 160.0 # default=150 (Ry)
scf.maxIter 70 # default=40
scf.EigenvalueSolver cluster # Recursion|Cluster|Band
scf.Kgrid 1 1 1 # means n1 x n2 x n3
scf.Mixing.Type rmm-diisk # Simple|Rmm-Diis|Gr-Pulay
scf.Init.Mixing.Weight 0.010 # default=0.30
scf.Min.Mixing.Weight 0.001 # default=0.001
scf.Max.Mixing.Weight 0.050 # default=0.40
scf.Mixing.History 7 # default=5
scf.Mixing.StartPulay 20 # default=6
scf.criterion 1.0e-8 # default=1.0e-6 (Hartree)

#
# 1D FFT
#

1DFFT.NumGridK 900 # default=900
1DFFT.NumGridR 900 # default=900
1DFFT.EnergyCutoff 3600.0 # default=3DFFT.EnergyCutoff*3.0 (Ry)

#
# Orbital Optimization
#

orbitalOpt.Method off # Off|Unrestricted|Restricted
orbitalOpt.InitCoes Symmetrical # Symmetrical|Free
orbitalOpt.initPrefactor 0.1 # default=0.1
orbitalOpt.scf.maxIter 30 # default=12
orbitalOpt.MD.maxIter 20 # default=5
orbitalOpt.per.MDIter 2 # default=1000000
orbitalOpt.criterion 1.0e-4 # default=1.0e-4 (Hartree/borh)^2

#
# output of contracted orbitals
#

CntOrb.fileout off # on|off, default=off
Num.CntOrb.Atoms 1 # default=1
<Atoms.Cont.Orbitals
1
Atoms.Cont.Orbitals>

#
# SCF Order-N
#

orderN.HoppingRanges 6.3 # default=5.0 (Ang)
orderN.NumHoppings 2 # default=2
orderN.KrylovH.order 500 # default=400
orderN.recalc.EM off

#
# restart using *.rst
#

scf.restart off # on|off, default=off


#
# MD or Geometry Optimization
#

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)

#
# Band dispersion
#

Band.dispersion off # on|off, default=off
# if <Band.KPath.UnitCell does not exist,
# the reciprical lattice vector is employed.
Band.Nkpath 5
<Band.kpath
15 0.0 0.0 0.0 1.0 0.0 0.0 g X
15 1.0 0.0 0.0 1.0 0.5 0.0 X W
15 1.0 0.5 0.0 0.5 0.5 0.5 W L
15 0.5 0.5 0.5 0.0 0.0 0.0 L g
15 0.0 0.0 0.0 1.0 1.0 0.0 g X
Band.kpath>

#
# MO output
#

MO.fileout off # on|off
num.HOMOs 1 # default=2
num.LUMOs 1 # default=2

MO.Nkpoint 1 # default=1
<MO.kpoint
0.0 0.0 0.0
MO.kpoint>

#
# DOS and PDOS
#

Dos.fileout off # on|off, default=off
Dos.Erange -20.0 20.0 # default = -20 20
Dos.Kgrid 12 12 12 # default = Kgrid1 Kgrid2 Kgrid3


HS.fileout on # on|off, default=off
=====================================================================================
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Re: Binding energy calculation ( No.1 )
Date: 2006/10/12 23:05
Name: T.Ozaki

Hi,

Could you check the standard output ?
If you see "The system is molecule." in the standard output,
it is Okay. But I wonder that the part "molecule" can be
"chain", "slab", or "bulk", since the cutoff radius of basis function
for W is long. Then, the "molecular calculation" you intend becomes
the band calculation. The cell size should be determined by the largest
distance between atoms you try, and should be fixed during the calculation of
energy curve. Otherwise, you will have some artifact effect arising from
the unit cell size.

Also, the pseudopotential of W is a deep one. Thus, the dependency on
"scf.energycutoff" should be checked carefully.

As for O2 case, with above things the basis set convergence should be
checked. Elements in the sixth and seventh columns tend to requires
a large number of basis function for the convergence.

You can find the convergence properties of the O2 bond length with
respect to basis functions in
Phys. Rev. B 69, 195113 (2004).
http://netserver.aip.org/cgi-bin/epaps?ID=E-JCPSA6-121-301439

Regards,

TO
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