Large value for SMASS with large value for Sigma

[comorado]

Hello,

I was doing MD simulation of be super cell with 386 atoms.

First I was doing calculations with IONIC temperature of (~ 2eV) (TEEND = 23209) and my SMASS=22.0, which would give the right value for Nose freq. Nose-frequenzy (Omega) = 0.10E+15

After turning on

ISMEAR = -1
SIGMA = 2.00 #(2eV electronic temperature)

I had to increase SMASS = 930.0 to have the same reported Nose-frequenzy (Omega) = 0.10E+15.

This big of adjustment for SMASS is suprising to my experties, and I would like to know if it does make sense that one needs to increaser SMASS parameter if SIGMA is changed.

old INCAR
################
System = Be 6x4x4 repetition of orthogonal cell

PREC = Medium

ISMEAR = 0
SIGMA = 0.05

IALGO = 48 ! RMM-DIIS algorithm for electrons
LREAL = A ! evaluate projection operators in real space
NELMIN = 4 ! do a minimum of four electronic steps
BMIX = 2.0 ! mixing parameter
MAXMIX = 50 ! keep dielectric function between ionic movements

LPLANE = .TRUE.
NPAR = 72
LSCALU = .FALSE.
NSIM = 8

ISYM = 0

NSW = 800
SMASS = 22.00
POTIM = 0.50
TEBEG = 23209

ISTART = 1
ICHARG = 1
########################
New INCAR
#########################
System = Be 6x4x4 repetition of orthogonal cell

PREC = Medium

ISMEAR = -1
SIGMA = 2.00

IALGO = 48 ! RMM-DIIS algorithm for electrons
LREAL = A ! evaluate projection operators in real space
NELMIN = 4 ! do a minimum of four electronic steps
BMIX = 2.0 ! mixing parameter
MAXMIX = 50 ! keep dielectric function between ionic movements

LPLANE = .TRUE.
NPAR = 72
LSCALU = .FALSE.
NSIM = 8

ISYM = 0

NSW = 700
SMASS = 930.00
POTIM = 0.50
TEEND = 23209

ISTART = 1
ICHARG = 1
##################################

Thank you!

[Neutrino]

Hi comorado,

The temperatures you are simulating are very very high and Born-Oppenheimer approximation definitely does not hold in this case, that is to say it is highly questionable to perform Born-Oppenheimer at such temperature.

I believe at moderate temperatures, you should not observe any relation between SMASS and the smearing.


Mostafa

[comorado]

I found the problem, I have specified in one case TEEND and TEBEG in the second case. If I change to TEBEG it works fine.