Hi,

I recently encountered a problem with adding electric field on a ccsd energy calculation.

The problem is that when I used the following input, the perturbation would be already added in SCF calculation, which is not what I want. (I just need the unrelaxed orbitals from SCF calculation and conduct ccsd energy calculation with perturbation.)

molecule mol {

0 1

C .0000030150 .0000036400 .0000139900

H 1.0962824850 .0002186300 .0088333700

H -.3657450550 1.0334718700 .0088329700

H -.3725226950 -.5271066900 .8861702200

H -.3580328250 -.5066056500 -.9039205000

symmetry c1

no_reorient

no_com

}

set {

basis d-aug-cc-pVDZ

guess sad

scf_type direct

freeze_core true

df_basis_scf d-aug-cc-pvdz-jkfit

e_convergence 5.0E-10

d_convergence 5.0E-10

r_convergence 5.0E-9

}

pert = 3.7794522500e-5

set perturb_h true

set perturb_with dipole

set perturb_dipole [$pert, 0, 0]

energy(‘ccsd’)

However, when I change the input to the following, the calculation didn’t take the perturbation at all, the output was the same as the one without any perturbation setting…

…

scf_e, scf_wfn = energy(‘scf’, return_wfn=True)

pert = 3.7794522500e-5

set perturb_h true

set perturb_with dipole

set perturb_dipole [$pert, 0, 0]

energy(‘ccsd’,ref_wfn=scf_wfn)

So does anyone know how to add the perturbation properly to a ccsd energy calculation? Thanks a lot!