Hello

Are there any known problems with running TD-DFT calculations using multiple processing threads?

I noticed some inconsistencies some time ago and just ignored it. But going through some old calculations I rediscovered it and thought I would run some tests. I ran the same problematic input file once with no thread specifier, once with “-nt 2” and once with “-nt 4”.

The single-threaded calculation runs great. The calculations using OpenMP both have approx 10x the number of CIS iterations before converging, and the first ~30 excited states have negative energies with a strength of 0. The SCF calculation converges on the same energy (in the same number of cycles) in all 3 calculations.

My rem section looks like this:

$rem

BASIS = 6-311G**

CIS_N_ROOTS = 100

CIS_MAX_CYCLES = 200

CIS_TRIPLETS = 0

EXCHANGE = SRC2-R1

GUI = 2

N_SOL = 2

TDDFT_FAST = 1

TRNSS = 1

TRTYPE = 3

$end

The calculation is a N K-edge XAS simulation on an organic molecule with around 40 atoms.

I am happy to continue testing… my next step will be to repeat the same input file without TDDFT_FAST (as I realize this isn’t an “official” feature). But figured I would post here before narrowing it down in case this is a known issue?

I am using Qchem 5.3 locally on a windows machine.

Thank for all the help