VASP Forum

Hello,

I am trying to compare the outputs of TDHF and TIMEEV runs (with VASP 6.6.1). The VASP Wiki indicates that, to bring the Casida results into closer agreement with time-propagation, one should increase ENCUTGW beyond its default value and set ANTIRES=2 in the Casida TDDFT calculation.

As an example, for a TDHF run that uses ENCUT=450 eV, the OUTCAR shows ENCUTGW=300 eV, and ENCUTGWSOFT=240 eV (exactly as per the defaults noted on the Wiki).

On the other hand, for the TIMEEV run, the output is a bit more cryptic: for ENCUT = 450 eV, the OUTCAR shows ENCUTGW=-1.6 and ENCUTGWSOFT=-1.6 -- it is not immediately obvious what the actual values are and, consequently, I am not able to port these defaults to the Casida run for consistency.

Any clarification is most appreciated!

Ashwin

Dear Ashwin,

ENCUTGW and ENCUTGWSOFT are set to -1.6 by construction in the TIMEEV run. Since these are not specified in the INCAR, VASP internally initialises them to -2 (meaning "not set by the user"), and later some safeguards multiply them by 0.8, hence the -1.6 value you observe.

The TIMEEV algorithm does not use ENCUTGW nor ENCUTGWSOFT. The Hartree and exchange parts of the Hamiltonian in TIMEEV are built using the same Hartree-Fock routines that are used for ground-state/hybrid functional calculations. The cutoffs are controlled by ENCUT/PRECFOCK/ENCUTFOCK. So there is no equivalent to ENCUTGW or ENCUTGWSOFT that you can use in the INCAR in the TDHF run.

Essentially you are performing a convergence run. You need to increase the value of ENCUTGW until the spectrum stops changing. The advice here is to perform this on a job where all the other parameters are not converged, (NBANDSO, NBANDSV, KPOINTS, etc). This will make your jobs faster and require fewer resources.

Hope this helps. Kind regards,
Pedro

Thanks for the clarification, Pedro.

How come the OUTCAR and standard output display this warning for TIMEEV: "The default for ENCUTGWSOFT is different in this version of VASP. If you wish to obtain identical results as using pre vasp.6.3 please manually set ENCUTGWSOFT =-2 in the INCAR file."? Based on what you noted, I assume that this can be ignored, correct?

Ashwin