Calculation Not Converging

[kmkumar]

Hi All,

I have problem in one of my calculation.
I set up NSW=220 and upto 50 iterations, the energy get decreased,
but after that it remains the same for the remaining upto 220 steps.
I find that the calculation is not towards convergence.

I post my INCAR here

------------------
System = silico di oxide

! 0=new, 1=wave (d), 2=same cutoff&latt (1&2 need WAVECAR file)
ISTART=1
! 0=wave (d), 1=CHGCAR
ICHARG=1

NPAR = 8
! how is parallelization done
LPLANE = .TRUE.

ENCUT= 400.00 eV
ENAUG= 700.00 eV


LREAL = auto
! use real space projection of PPs
!ROPT = 2e-4 2e-4
! prec of real space projection; repeat for each species
PREC = Accurate
! sets cutoff and FFT grid; Normal | Accurate | High; if High, sets ROPT=2e-4 automatically
ALGO = Fast
NSIM =5
! RMM-DIIS algorithm (IALGO=48) works in a blocked mode; NSIM bands are optimized at the same time. This allows to use matrix-matrix operations instead of matrix-vector operation for the evaluations of the non local projection operators in real space, and might speed up calculations on some machines

! wrap-around error warned
NGX = 66
NGY = 66
NGZ = 269

ENMAX=400

!IDIPOL = 4

NBANDS = 600
!NELM = 100
EDIFF=1e-5 ! converge force better

ISMEAR=0
SIGMA=0.01

ISPIN=2
!MAGMOM=2 2 2 2 2 2 2 2
!ISIF = 2 ! 0: relax ions, 1,2:relax ions,calc stresses, 3:relax ion+cell
NUPDOWN=0

NSW=220 !!!! Do not relax for now !!!
IBRION = 2 ! 1: quasi-NR, 2: CG algorithm for ions; use 2 for first run
!POTIM = 0.4 ! time step
EDIFFG=-0.05
!NFREE = 10 ! number of DIIS vectors to save

! write wavefunction
LWAVE=.TRUE.
! write chg and chgcar
LCHARG=.TRUE.

------------------

i post my section of OSZICAR (Even after 43 cycles)
it starts oscillating.


37 F= -.91201753E+03 E0= -.91201326E+03 d E =0.117839E+03 mag= 0.0000
38 F= -.91206963E+03 E0= -.91206538E+03 d E =0.117787E+03 mag= 0.0000
39 F= -.93866492E+03 E0= -.93866107E+03 d E =0.911913E+02 mag= 0.0000
40 F= -.10409960E+04 E0= -.10409958E+04 d E =-.111398E+02 mag= 0.0000
41 F= -.91270778E+03 E0= -.91270373E+03 d E =0.128288E+03 mag= 0.0000
42 F= -.91218044E+03 E0= -.91217619E+03 d E =0.128816E+03 mag= 0.0000
43 F= -.91218047E+03 E0= -.91217625E+03 d E =0.128816E+03 mag= 0.0000
44 F= -.91218116E+03 E0= -.91217695E+03 d E =0.128815E+03 mag= 0.0000
45 F= -.91218140E+03 E0= -.91217729E+03 d E =0.128815E+03 mag= 0.0000
46 F= -.91218162E+03 E0= -.91217742E+03 d E =0.128814E+03 mag= 0.0000
47 F= -.91218170E+03 E0= -.91217749E+03 d E =0.128814E+03 mag= 0.0000
48 F= -.91218172E+03 E0= -.91217750E+03 d E =0.128814E+03 mag= 0.0000
49 F= -.91218175E+03 E0= -.91217752E+03 d E =0.128814E+03 mag= 0.0000
50 F= -.91218177E+03 E0= -.91217771E+03 d E =0.128814E+03 mag= 0.0000
51 F= -.91218177E+03 E0= -.91217755E+03 d E =0.128814E+03 mag= 0.0000
52 F= -.91218177E+03 E0= -.91217766E+03 d E =0.128814E+03 mag= 0.0000
53 F= -.91218177E+03 E0= -.91217756E+03 d E =0.128814E+03 mag= 0.0000
54 F= -.91218177E+03 E0= -.91217760E+03 d E =0.128814E+03 mag= 0.0000
55 F= -.91218177E+03 E0= -.91217756E+03 d E =0.128814E+03 mag= 0.0000
56 F= -.91218177E+03 E0= -.91217757E+03 d E =0.128814E+03 mag= 0.0000
57 F= -.91218177E+03 E0= -.91217757E+03 d E =0.128814E+03 mag= 0.0000
58 F= -.91218177E+03 E0= -.91217759E+03 d E =0.128814E+03 mag= 0.0000
59 F= -.91218177E+03 E0= -.91217756E+03 d E =0.128814E+03 mag= 0.0000
60 F= -.91218177E+03 E0= -.91217758E+03 d E =0.128814E+03 mag= 0.0000
61 F= -.91218177E+03 E0= -.91217759E+03 d E =0.128814E+03 mag= 0.0000
62 F= -.91218177E+03 E0= -.91217757E+03 d E =0.128814E+03 mag= 0.0000
63 F= -.91218177E+03 E0= -.91217757E+03 d E =0.128814E+03 mag= 0.0000

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Any suggestions would be appreciated.

Best regards,
Muthu

[boris]

Hi

It often happens with a convergence criteria on forces. Maybe you should set EDIFFG to 1E-6 instead of a negative value, so that the convergence criteria be on the total energy difference instead of the forces.

According to your OSZICAR file, it seems to me that the total energy is converged. But there's not enough digit to be sure.

Regards