Convergence problem

[Jiaye Li]

Dear all

A problem has bewindered me for a long time. I set up a calculation on SiO2 surface, while after adding O2 onto the surface, I found that the SCF didn't converge (I set the maximum as 250). This is my INCAR, would anybody help me? Thanks.

SYSTEM = Silicon Oxide surface
Startparameter for this Run:
NWRITE = 2 verbosity write-flag
LPETIM= F write-flag & timer #
ISTART = 0 0-new 1-cont 2-samecut job
ISPIN = 1 1-no, 2-yes
INIWAV = 1 0-jellium WF; 1-random numbers (recomm.)

Electronic Relaxation
! ENCUT = 400.00 #Ecut (eV)
PREC = Medium * #precission: #Low/Medium/High
NELM = 150 max. # of electronic SC steps
NELMDL = 5 # of non-consistent steps at the beggining:>0 or <0
EDIFF = 1.0e-4 stopping-criterion for electronic upd.
VOSKOWN = 1
ISMEAR = -5
SIGMA = 0.1
AMIX = 0.2
BMIX = 0.0001

Ionic relaxation
EDIFFG = 1.0e-3 stopping-conditions for ionic relax.loop (EDIFF*10)
NSW = 250 * # of steps for ionic update (def:0)
IBRION = 2 * ionic relax: -1:no move; 0-MD;1-Newton;2-CG;3-damped;4-?
ISIF = 2 * calc.stress:0-no;1-tr;2-7 yes; 3-change vol.4-change shape
! ISYM = 2 symmetry:0-OFF, 1-ON,2-ON+memory conserving for CD
NBLOCK = 1
POTIM = 0.3 if IBRION=1,2,3:scaling constant forces;IBRION=0,time st.


! LPLANE = .TRUE.
! NPAR = 8
IALGO = 48 * algorithm: use only 8 (CG) or 48 (RMM-DIIS)
LDIAG = .TRUE. sub-space diagonalisation
GGA = 91 * xc-type: PB, PW (86), LM, 91 (Perdew-Wang 91)

LWAVE = .T. * write WAVECAR
LCHARG = .T. * write CHGCAR and CHG
LVTOT = .T. * write the local potential LOCPOT
LELF = .F. create ELFCAR file
LORBIT = .F. create PROOUT
LREAL = Auto

[admin]

1) EDIFF=1e-4 probably is not small enough to achieve sufficient electronic convergence to obtain reliable forces (please use 1e-6)
2) please don't set LVTOT for the scf-runs.
3) have you checked whether the slab has a net dipole moment? If so, please set IDIPOL=3
4) have you checked the k-point convergence and made sure that your k-mesh includes Gamma and points at the edge of the BZ (for BZ integration using the Tetahedron method)?

[Jiaye Li]

Thank you very much. I will take a try again.