CIPSI 2-state calculations¶

Import Wavefunction¶

Import the single-determinant wavefunction from the TREXIO file:

qp_import_trexio.py COH2.trexio -o COH2
qp set_file COH2

Configure QP to seek two states:

qp set determinants n_states 2
qp set determinants n_det_max 2000

First, perform a CIS calculation to ensure we capture states of different symmetries (Ground State and Excited State):

qp run cis | tee COH2.cis.out

Now, refine the wavefunction using CIPSI (FCI in truncated space). We use a selection factor to carefully grow the determinant space:

qp set determinants selection_factor 0.5
qp set determinants read_wf true
qp run fci | tee COH2.fci.out

Check COH2.fci.out. You should see two states with an excitation energy around 4 eV.