Quantum Package and CHAMP : Excited States Calculation
We will import a Hartree-Fock wavefunction for the formaldehyde (\(COH_2\)) molecule from a TREXIO file into Quantum Package (QP), and run a two-state CIPSI calculation with these orbitals. The wavefunctions for the 2 states will be stored in the TREXIO file, and we will run wave function optimization in CHAMP, followed by a Diffusion Monte Carlo calculation.
The theoretical best estimate of the excitation energy (complete basis set extrapolation from coupled cluster calculations) is 3.97 eV.