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geometry optimization problem
Date: 2008/11/04 00:02
Name: Yuzheng Guo

Steepest decent optimization is used to find the minimum energy in a large super cell.
However sometimes the energy and force will have a sudden large increase:
---------------------------------------------------------
MD_iter SD_scaling |Maximum force| Maximum step Utot
73 2.51554024 0.00948052 0.01262015 -11142.90310599
74 2.51554024 0.00927013 0.01234009 -11142.90553023
75 2.51554024 0.00944966 0.01257907 -11142.90802843
76 2.51554024 0.00967166 0.01287459 -11142.91169641
77 3.01864829 0.01021463 0.01631685 -11142.91426104
78 3.01864829 0.01220600 0.01949787 -11142.92500751
79 3.01864829 0.96178986 1.53636312 -11107.12602026
80 3.01864829 2.67706198 4.27633880 -11107.16899469
81 0.75466207 66.38256664 26.50987793 -11057.45364218
82 0.75466207 46.77610004 18.68003551 -11100.66550706
83 0.75466207 55.37926956 22.11571125 -11111.64298766
84 0.75466207 3.91499889 1.56345481 -11127.04855713
85 0.90559449 1.75866415 0.84278703 -11130.64075227
86 0.90559449 0.50638261 0.24266867 -11134.48035956

-------------------------------------------------------
My super cell is 128 Fe atoms with random position distribution:
Fe Fe4.5opt-s1p2d1 Fe_GGA7
The input file is attached below.
The only possible reason is that perhaps the MDstep(1fs) is too large.
But I suppose that steepest decent method will not use MD step.
According to my knowledge there should be some parameter to control the trial step in this method but I did not found it in the manual.

Could anyone shed some lights on this problem?
Thanks.

Yuzheng Guo



-------------------------------------------------------
scf.XcType GGA-PBE # LDA|LSDA-CA|LSDA-PW
scf.SpinPolarization on # On|Off
scf.partialCoreCorrection On # On|Off
scf.ElectronicTemperature 300.0 # default=300 (K)
scf.energycutoff 100.0 # default=150 (Ry)
#scf.Ngrid 32 32 32
scf.maxIter 100 # default=40
scf.EigenvalueSolver band # 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 0.30 # default=0.30
scf.Min.Mixing.Weight 0.001 # default=0.001
scf.Max.Mixing.Weight 0.400 # default=0.40
scf.Mixing.History 7 # default=5
scf.Mixing.StartPulay 13 # default=6
scf.criterion 1.0e-9 # default=1.0e-6 (Hartree)

#
# 1D FFT
#

1DFFT.NumGridK 900 # default=900
1DFFT.NumGridR 900 # default=900
1DFFT.EnergyCutoff 3600.0 # default=3600(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 9.2 # default=5.0 (Ang)
orderN.NumHoppings 3 # default=2
orderN.KrylovH.order 600 # default=400
orderN.recalc.EM off

#
# restart using *.rst
#

scf.restart on


#
# MD or Geometry Optimization
#

MD.Type Opt # Nomd|Opt|DIIS|NVE|NVT_VS|NVT_NH
MD.maxIter 100 # default=1
MD.TimeStep 1 # default=0.5 (fs)
MD.Opt.criterion 1.0e-4 # default=1.0e-4 (Hartree/bohr)

#
# Band dispersion
#

Band.dispersion off # on|off, default=off
<Band.KPath.UnitCell
3.56 0.00 0.00
0.00 3.56 0.00
0.00 0.00 3.56
Band.KPath.UnitCell>
# 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 off # on|off, default=off
e
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