For my current project I need the converged CHGCAR results for sets of ions.
For light atoms this goes reasonably well (first row elements)...and also for some heavier elements not to many problems are observed. However, for the Ce ions I seem to have no luck in getting the calculation to converge.
I'm using a cubic 20.5x20.5x20.5Angstrom cell a gamma centered K-point and the following INCAR file:
! Run VASP twice using this INCAR to get the
! groundstate energy of single atoms (10.5 manual)
general:
SYSTEM = Ce atom
ISTART = 0 ! start from 0: scratch, 1: previous WAVECAR
ENCUT = 500 ! ENCUT for O
LWAVE = .FALSE.
LCHARGE = .TRUE.
LVTOT = .FALSE.
NBANDS = 24 ! fix number of bands manually
EDIFF = 1.0E-8
PREC = High
LASPH = .TRUE. ! because magnetic between B and F
NUPDOWN = 2 ! the exact ionisation of the neutral Ce ion
!molecule:
LDIPOL = .TRUE.
IDIPOL = 4
cohesive:
ISYM = 0 ! no symmetry
ISPIN = 2 ! allow for spinpolarisation
VOSKOWN = 1 ! this is important, in particular for GGA
ISMEAR = 0 ! Gaussian smearing, otherwise negative occupancies
SIGMA = 0.10 ! intermid. smearing width
AMIX = 0.2 ! set mixing manually
BMIX = 0.0001
NELM = 40 ! 40 electronic steps
ICHARG = 1 ! use previous CHGCAR
dynamic:
IBRION = -1 ! -1: Fix atoms; 0: MD; 2: ConjGrad relax
NSW = 0 ! Number electronic steps
parallel:
LPLANE = .TRUE.
NPAR = 1
NSIM = 1
!LDIAG = .FALSE.
extra helpers:
NGXF = 210 ! 20x20x20 A cell?
NGYF = 210
NGZF = 210
NELECT = 12
a resulting OSZICAR:
N E dE d eps ncg rms rms(c)
DAV: 1 0.993402507473E+02 0.99340E+02 -0.12397E+03 108 0.131E+02
DAV: 2 0.137464764246E+02 -0.85594E+02 -0.77931E+02 146 0.515E+01
DAV: 3 0.899603259351E+00 -0.12847E+02 -0.86820E+01 160 0.267E+01
DAV: 4 -0.104561323103E+01 -0.19452E+01 -0.19592E+01 152 0.951E+00
DAV: 5 -0.121318007347E+01 -0.16757E+00 -0.66342E-01 142 0.224E+00 0.446E+00
DAV: 6 -0.138070174447E+01 -0.16752E+00 -0.31362E-01 134 0.222E+00 0.256E+00
DAV: 7 -0.142141215306E+01 -0.40710E-01 -0.34476E-02 120 0.758E-01 0.264E+00
DAV: 8 -0.141285326016E+01 0.85589E-02 -0.12687E-01 120 0.127E+00 0.135E+00
DAV: 9 -0.144941885177E+01 -0.36566E-01 -0.14692E-02 120 0.539E-01 0.164E+00
DAV: 10 -0.146074291525E+01 -0.11324E-01 -0.90256E-03 114 0.435E-01 0.205E+00
DAV: 11 -0.145456842544E+01 0.61745E-02 -0.23473E-03 112 0.244E-01 0.277E+00
DAV: 12 -0.144509799772E+01 0.94704E-02 -0.28615E-03 104 0.295E-01 0.279E+00
DAV: 13 -0.143805037978E+01 0.70476E-02 -0.75565E-03 110 0.472E-01 0.204E+00
DAV: 14 -0.144323956864E+01 -0.51892E-02 -0.16872E-03 102 0.239E-01 0.181E+00
DAV: 15 -0.145132781123E+01 -0.80882E-02 -0.16322E-03 104 0.229E-01 0.166E+00
DAV: 16 -0.145703170139E+01 -0.57039E-02 -0.33766E-03 108 0.342E-01 0.143E+00
DAV: 17 -0.146632548371E+01 -0.92938E-02 -0.48678E-03 100 0.347E-01 0.795E-01
DAV: 18 -0.147729024011E+01 -0.10965E-01 -0.15725E-03 100 0.206E-01 0.722E-01
DAV: 19 -0.147931342726E+01 -0.20232E-02 -0.56082E-04 98 0.134E-01 0.845E-01
DAV: 20 -0.147849561970E+01 0.81781E-03 -0.55328E-04 98 0.129E-01 0.102E+00
DAV: 21 -0.147759179930E+01 0.90382E-03 -0.20389E-03 104 0.239E-01 0.116E+00
DAV: 22 -0.147491013021E+01 0.26817E-02 -0.10690E-03 104 0.176E-01 0.135E+00
DAV: 23 -0.147185709952E+01 0.30530E-02 -0.91042E-04 106 0.150E-01 0.172E+00
DAV: 24 -0.146618254916E+01 0.56746E-02 -0.45111E-04 100 0.103E-01 0.215E+00
DAV: 25 -0.146360388305E+01 0.25787E-02 -0.74580E-04 104 0.134E-01 0.282E+00
DAV: 26 -0.145549406639E+01 0.81098E-02 -0.69390E-04 102 0.132E-01 0.318E+00
DAV: 27 -0.144810948641E+01 0.73846E-02 -0.30536E-04 114 0.834E-02 0.338E+00
DAV: 28 -0.144165169082E+01 0.64578E-02 -0.26756E-04 110 0.773E-02 0.337E+00
DAV: 29 -0.143986329627E+01 0.17884E-02 -0.37679E-05 104 0.278E-02 0.339E+00
DAV: 30 -0.143908305972E+01 0.78024E-03 -0.45740E-05 106 0.327E-02 0.338E+00
DAV: 31 -0.143964263245E+01 -0.55957E-03 -0.68446E-04 102 0.101E-01 0.346E+00
DAV: 32 -0.144006094015E+01 -0.41831E-03 -0.18352E-04 110 0.543E-02 0.365E+00
DAV: 33 -0.143672650214E+01 0.33344E-02 -0.13062E-04 98 0.556E-02 0.372E+00
DAV: 34 -0.143536114308E+01 0.13654E-02 -0.17750E-04 102 0.611E-02 0.382E+00
DAV: 35 -0.143429071704E+01 0.10704E-02 -0.34711E-05 114 0.291E-02 0.388E+00
DAV: 36 -0.143310371580E+01 0.11870E-02 -0.17922E-05 96 0.202E-02 0.391E+00
DAV: 37 -0.143181828509E+01 0.12854E-02 -0.41810E-05 106 0.297E-02 0.392E+00
DAV: 38 -0.143160051302E+01 0.21777E-03 -0.68982E-06 112 0.131E-02 0.393E+00
DAV: 39 -0.143037712179E+01 0.12234E-02 -0.79349E-05 96 0.509E-02 0.387E+00
DAV: 40 -0.142901819784E+01 0.13589E-02 -0.55622E-04 106 0.115E-01
1 F= -.14290182E+01 E0= -.14074767E+01 d E =-.430830E-01 mag= 2.0000
whatever I seem to be trying I never get a better convergence than 10-2 in my OSZICAR file.
I have tried starting from a converged non-spinpolarized calculation (which actually show even worse convergence), I have tried switching on and of the LDIAG tag, and set NSIM to 1 (previous it was
.Changes of the value for SIGMA have no serious influence.
I have enough BANDS to nicely contain all the electrons present, and I am now also out of ideas of what to change.
The above calculations are all using the PBE potential.
anybody any ideas of how else I might force these ions into convergence?(I generaly have sets going from X^+5 .. X^-2 ions.
Danny
<span class='smallblacktext'>[ Edited ]</span>