Is my setting of parallelization correct?

[Vinco2022]

For the following input

molecule n2 {
  0 1
  H      1.2194     -0.1652      2.1600
  C      0.6825     -0.0924      1.2087
  C     -0.7075     -0.0352      1.1973
  H     -1.2644     -0.0630      2.1393
  C     -1.3898      0.0572     -0.0114
  H     -2.4836      0.1021     -0.0204
  C     -0.6824      0.0925     -1.2088
  H     -1.2194      0.1652     -2.1599
  C      0.7075      0.0352     -1.1973
  H      1.2641      0.0628     -2.1395
  C      1.3899     -0.0572      0.0114
  H      2.4836     -0.1022      0.0205
}

set {
  reference   rhf
  scf_type pk
  basis cc-pVDZ
  guess gwh
}


psi4.core.set_num_threads(2)
psi4.set_memory('1GB')

energy('ccsd(t)')

with psi4 1.6.11, the output includes

    Memory:     500.0 MiB
    Threads:    1
...
 Threads set to 2 by Python driver.

  Memory set to 953.674 MiB by Python driver.

and the wall times are

psi4.core.set_num_threads(1) Psi4 wall time for execution: 0:04:37.55
psi4.core.set_num_threads(2) Psi4 wall time for execution: 0:05:49.89

Hence, I would like to know if my setting on parallelization is correct. If not, how to make it right? Thank you very much.

[susilehtola]

Hi, the input looks correct to me.

I just wanted to note that guess gwh is the worst guess available in Psi4, see https://doi.org/10.1021/acs.jctc.8b01089

In your example, GWH requires 12 SCF iterations whereas the default SAD guess only needs 6 in Psi4 1.3.2. (Newer versions of Psi4 have better SCF algorithms so YMMV)

The default guess, sad, usually gets you the best convergence. If sad does not work, sap and huckel offer reasonable alternatives.