optimization of the surface-dye complex

Message

imsam100 · #1 Post by **imsam100** » Thu Apr 23, 2009 9:49 am

Hello VASP users,
I am trying to optimize a surface-dye complex (total 140 atoms) with PAW potentials using following input in INCAR file:

PREC = Accurate ! medium precision
EDIFF = 1e-4 ! electron relaxation criteria
EDIFFG = 1e-3 ! ion relaxation criteria
ENCUT = 400 ! Energy cutoff
ISIF = 2 ! internal coordinates relaxation
IBRION = 2 ! CG
POTIM = 0.1
ICHARG = 2 ! superposition of atomic charge densities as initial density
ISYM = 2 ! memory conserving symmetry calculation
NSW = 300 ! maximum ion relaxation steps

ISMEAR = 0 ! Gaussian smearing
SIGMA = 0.01 ! width of smearing in eV

ALGO = Normal ! mixed algorism with Davidson and RMM-DIIS

LWAVE = F ! Save wave function
LCHARG = F ! Save charge densities
LREAL = auto ! Real space projection
SYMPREC = 1e-6

The optimization was running for 4 days on 64 processors, But is is not showing convergence.

Do I need to make some corrections in the INCAR file?
Can we freeze surface atoms of the complex?

Any suggestion would be of great help.

Sincere regards,

Saurabh

Danny · #2 Post by **Danny** » Tue May 12, 2009 1:21 am

How many ionic steps do you have?
Do you get any errors?(in standard output, not OUTCAR--> sigma could be to small then)
Do the number of electronic steps decrease per ionic step of do they remain the same(and how many? 60 or 10-20, If you get 60 then there is a problem with the electronic convergence already)

EDIFF might be a bit small (I tend to use 1.0E-5 and 1.0E-6, even for 200 atoms/cell)

You can try a different ALGO (use the standard one instead of the RMM-DIIS)

wrt freezin atoms...that depends on how strong your interactions are, how easily is your surface modified?

can you post some output?(OSZICAR) that might help identify some problem.

Danny

Danny · #3 Post by **Danny** » Tue May 12, 2009 1:23 am

PS: us a viewer like p4vasp to check the change of the forces during the relaxation, and how the atoms move, this might also give you a clue as to the cause of your problem...it could be that your starting-guess is just really bad...or that you systems goes back and forth between two geometries...