Dear all,
I am doing structural relaxation of a rock salt (but in close-packed form, hexagonal) 107-atom PbS supercell containing one Pb vacancy. The relaxation steps are as follows:
1. ISIF=2, KPOINTS=Gamma-point only
2. ISIF=2, KPOINTS=Gamma-centered 2x2x2
3. ISIF=2, KPOINTS=Gamma-centered 4x4x4
4. ISIF=3, KPOINTS=Gamman-centered 4x4x4
But the converged energy for each steps are jumping:
1. -233.27933023
2. -232.28252864
3. -232.07779428
4. -232.06740704
In another case, I found the energies are STEP 1< STEP 2< STEP 3< STEP4, which is really strange. Because how come the the energy with poorer settings is lower than the one from a higher-setting calculation?
Hopefully some experienced users can solve my puzzle. Thank you in advance!
PS. The INCAR for STEP 1 is attached below. Please inform me if you need more information.
Regards,
Murphy
=====================================================
INCAR for STEP 1:
# Startparameter for this run:
PREC = high
NPAR = 4
# Electronic Relaxation 1
ENCUT = 500.0
ENAUG = 700.0
EDIFF = 0.00001
LREAL = A
NELM = 60
NELMIN = 2
NELMDL = 6 # of ELM steps
# Ionic relaxation
EDIFFG = -0.01 #stopping-criterion for IOM
NSW = 60 #number of steps for IOM
IBRION = 2 #ionic relax: 0-MD 1-quasi-New 2-CG
ISIF = 2
ISYM = 1 #0-nonsym 1-usesym 2-fastsym
POTIM = 0.5000 #time-step for ionic-motion
#DOS related values:
ISMEAR = 0
SIGMA = 0.05 #broadening in eV -4-tet -1-fermi 0-gaus
# Electronic relaxation 2 (details)
IALGO = 48 #algorithm
LMAXMIX = 4
# Dimension of arrays
NBANDS = 720
Energy jump in relaxation of PbS supercell containing one vacancy
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Energy jump in relaxation of PbS supercell containing one vacancy
Last edited by murphy on Wed Nov 06, 2013 5:33 pm, edited 1 time in total.
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Energy jump in relaxation of PbS supercell containing one vacancy
Energies from different settings are not comparable. Higher precision does not mean that the total energy is more negative.
Last edited by admin on Thu Nov 07, 2013 11:11 am, edited 1 time in total.