Hello all,

I’m running a RHF and CCSD calculation for H2O and trying to reproduce the 1-electron level energies (i.e. everything except the 2-electron repulsion) using the corresponding 1-electron density matrices and the K, V matrices like this.

```
grad, ccwfn = psi4.gradient('ccsd', return_wfn=True, ref_wfn=wfn)
mints = psi4.core.MintsHelper(ccwfn.basisset())
Da_cc = ccwfn.Da().to_array(copy=False, dense=True)
K = mints.ao_kinetic().to_array(copy=False, dense=True)
V = mints.ao_potential().to_array(copy=False, dense=True)
E_ke_cc = 2 * np.trace(np.matmul(K, Da_cc))
E_v_cc = 2 * np.trace(np.matmul(V, Da_cc))
```

The HF energies match the output file numbers. However the KE from the CCSD 1-RDM differs from the one in the output file by 1.69mH.

- Why aren’t they matching exactly (till floating point precision)?
- Also where can I find the CCSD potential (nuclear-electron) energy in the output file?

Here’s the full script which will print an output like the following.

Any help would be greatly appreciated. Thank you!

Energies from HF 1-RDM

Nuclear: 9.168193296424349

Kinetic: 74.58220348386018

Potential: -196.9063503606068

Coulomb: 47.29435182717615

Exchange: -9.101796533055854

Total : -74.96339828620196

Energies from CCSD 1-RDM

Nuclear: 9.168193296424349

Kinetic: 74.62366469678517

Potential: -196.82537980565303

Coulomb: 47.24918874993827

Exchange: -9.082702767239162

Total : -74.8670358297444