VASP-MD velocities and VACF

[graeme]

You can download the scripts here: https://theory.cm.utexas.edu/vtsttools/download.html

It should be compatible with vasp 6 - I don't know of any changes to the format of the XDATCAR.

[nidhit]

I have used the xdat2vdat.pl script from the link provided by you. Still, I am encountering differences between the kinetic energy values in the OUTCAR and VDATCAR files. The SMASS value is zero. Can you give any insights as to how the calculation of temperature and kinetic energies in OSZICAR differs from VDATCAR so that I can understand the reason behind the differences in the values. The .zip file of my calculation is attached herewith.

[nidhit]

I checked the code and found that the POMASS value from OUTCAR has been used for the mass of the respective atoms (which is the molar mass). In the line 93 of the script, these mass values have been stored without converting them into kg/atom. Is that the issue for the different kinetic energies and temperature in VDATCAR?

[graeme]

I will need some more guidance about the actual problem here. Everything should be molar mass, and I believe that it is.

[nidhit]

nidhit wrote:
> I have used the xdat2vdat.pl script from the link provided by you. Still, I
> am encountering differences between the kinetic energy values in the OUTCAR
> and VDATCAR files. The SMASS value is zero. Can you give any insights as to
> how the calculation of temperature and kinetic energies in OSZICAR differs
> from VDATCAR so that I can understand the reason behind the differences in
> the values. The .zip file of my calculation is attached herewith.


I have still not found the reason behind the differences in the values of K.E and T in OSZICAR and VDATCAR. Any discussion would be appreciated.

[nidhit]

From OSZICAR after first step:
T = 1400K and Ek = 0.5429 eV

From VDATCAR after first step:
KINETIC ENERGY (eV): 0.420320920660327
TEMP EFF (K): 1625.874061504934843

Could you kindly provide insight on whether the differences observed in the VDATCAR values are within acceptable limits, considering the initial data extracted from OSZICAR?

[graeme]

Temperatures and kinetic energy values are going to be controlled by a thermostat and so both values should fluctuate by Sqrt(N).