Dear everyone,
I have performed some AIMD simulation with vasp recently, but found that several initial structures always converge to very unreasonable structures. The detailed systems I modeled include one metal ion (UO22+ and Eu3+) and more 30 water or other sovent such as CH2Cl2, but after 1000 steps I observed terrible results. For examle, one NO3- ion lost one N atoms, or CH2Cl2 lost ether one H or one Cl.
Actually, the UO22+ U=O bond stretched to 2.06 eV after 1000 steps, which is much larger than the qm results. Could anyone gives some instructions about this situation?
one Gamma point is used, as well as PBE GGA method. The following is the parameters.
PREC = Normal
ENCUT = 400.000
EDIFF = 1.0e-04
EDIFFG = -0.02
IBRION = 0
NSW = 2000
POTIM = 1.0
SMASS = 1
TEBEG = 298.0
TEEND = 298.0
ISIF = 2
ISYM = 0
NELMIN=8
ALGO = 48
ISPIN = 2
LWAVE = .FALSE.
LCHARG = .FALSE.
ISMEAR = -1
SIGMA = 0.05
LREAL= Auto
NGX=64
NGY=64
NGZ=64
NUPDOWN=0
NELECT=424
APACO=10
NPACO=200
NBLOCK = 1
KBLOCK = 20
Mr./Miss/Mrs Lan,
I do not know how you have used VASP, but please find as attachment the theoretical levels and models for computation of Lns and Ans. It is shown an example of [UO2]2+ and [UO2]2+/acetonitrile systems, utilizing PCM and mixed solvation methods. The data have been obtained by Gaussian (http://www.gaussian.com/). The corresponding refs are provided as well.
I'm not familiar with your system, but from the parameters you listed, maybe you can try to make your time step smaller and see does the same thing happen?
Dear Yingdi,
I have tried different time step from 0.5 fs to 2 fs, but still obtained the same results. The new finding is that NUPDOWN causes these problem. If I comment out this parameter, the results come to be better. However, Eu is +3 charged with 6 unpaired electrons. Why did this parameter lead to bad results? Is there any suggestions?
By setting NUPDOWN=0 you are forcing the spin polarization of the system to some value, in your case 0. Better approach would be to use MAGMOM tag to set initial spin of every atom and then to allow VASP to relax to ground state (NUPDOWN=-1 which is default).
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