OpenCAP
Electronic structure of metastable states
Q-Chem Interface

Q-Chem is a widely used quantum chemistry package with a variety of open-shell and excited state electronic structure methods. We officially support an interface with EOM-CC calculations performed by Q-Chem. There is also an experimental TDDFT interface.

System

OpenCAP can extract the basis set from .fchk files generated by Q-Chem.

Relevant keywords

Keyword Valid options Description
molecule molden,rassi_h5,inline,qchem_fchk Specifies which format to read the molecular geometry. If "inline" is chosen, the "$geometry" section is also required.
basis_file path to basis file Specifies the path to the basis file. When "molecule" is set to "molden","rassi_h5", or "qchem_fchk", this keyword should be set to a path to a file of the specified type. When "molecule" is set to "inline", this keyword should be set to a path to a basis set file formatted in "Psi4" style.

Projected CAP

Densities can be read in from .fchk files, and the zeroth order Hamiltonian can be read from Q-Chem output files for EOM-CC calculations. To export the full densities to .fchk, GUI=2 must be set in the $rem card, and PROJ_CAP=3 must be set in the $complex_ccman card. See the Q-Chem manual for more details.

Separate alpha/beta densities and spin traced one particle densities are both supported, and are automatically detected by OpenCAP.

Relevant keywords

Keyword Type Description
qchem_fchk string Relative or absolute path to .fchk file containing TDMs.
qchem_output string Relative or absolute path to Q-Chem output file.
h0_file string Relative or absolute path to properly formatted zeroth order Hamiltonian file.

Example input

$system
molecule qchem_fchk
basis_file qc_input.fchk
$end

$projected_cap
method eom
package qchem
qchem_fchk qc_input.fchk
nstates 10
CAP_TYPE voronoi
R_CUT 3.00
Radial_precision  14
Angular_points    110
$end