My Community

Dear all,

I am doing optic calculations of carbon nanotubes. And my process is that:

1. doing a scf calculation with the following INCAR:
EDIFF=1E-6
ISMEAR= 0
SIGMA=0.05
ENCUT=450
2. read the old CHGCAR and WAVECAR and do a optic calculation without
scf, the new INCAR is:
ICHARG=11
EDIFF=1E-6
ISMEAR= 0
SIGMA=0.05
ENCUT=450
LOPTICS=.TRUE.
NPAR=1

Then I get a OPTIC file which contain the optic moment matrix.
However, I find that the CHG and CHGCAR file is rewritten and changed.

I diff the old and new CHG or CHGCAR files, and find something has been changed in these files.

Since I have set ICHARG=11, the charge density should not be changed.

The same thing happens when I calculate a Nb9 cluster.

However, for the system of GaAs and BaTiO3, the contents of CHG and CHGCAR do not change(although they also have been rewritten).

Is it because that I do not get a fine converged charge density of nanotube or cluster? But, I tested it in the GaAs, even for a not converged charge density, the CHG and CHGCAR files should not be changed when set ICHARG=11.

And then I am confused :-(

Thank you for your reading and hope you can give me some suggestions.

Best wishes.

jian

I have asked vasp master. and from his answer, the reason may be that:

The CHG file contain the real charge, which is charge density rho multiply the volume V. Since the V is quite large, a small numerical fluctuation of rho may cause a large fluctuation of charge in CHG file.

jian

I get the same result when I change ICHARG = 11.
: (
Please help me, I need to calculate OPTIC indeed.
Thanks.

sorry, I cannot reproduce this behaviour.

Dear admin:

I'm using the Nudged Elastic Band (NEB) method implemented by VASP. When the optimization of images is finished, at the end of OUTCAR file are printed three blocks.
The first block has six columns with the following heading:
POSITION TOTAL-FORCE (eV/Angst)
…… ……. …… …… ……. ……
…… ……. …… …… ……. ……
The second has six columns with the heading:
TANGENT CHAIN-FORCE (eV/Angst)
…… ……. …… …… ……. ……
…… ……. …… …… ……. ……
The last block has three columns with the heading:
CHAIN + TOTAL (eV/Angst)
…… ……. ……
…… ……. ……
I want to know what is the meaning of TOTAL-FORCE; of TANGENT; of CHAIN-FORCE…...
I suppose the numbers are connected with forces components?? But which forces are? Tangent to path? Normal to path? others one??

Thanks a lot for your answer