Excited States

Simulate > Excited States (MNDO-CI / MOM)... computes vertical excited states of a molecule, in the gas phase, at the geometry shown in the 3D view. Two methods are available, each in its own tab. The calculation runs in a separate process, so the interface stays responsive and the job can be cancelled.

Target

• Atoms: Selected molecule(s) (select the molecule first, for example with the selection mode Molecule) or Whole active system. Refresh updates the target after the selection changes.

• Charge and Ground-state multiplicity: suggested from the selected atoms; check them before running.

MNDO-CI tab

Configuration interaction with pDynamo's QCModelMNDOCI, on a reference with fractional HOMO/LUMO occupancy. It gives excitation energies only (no intensities).

• Hamiltonian: AM1, PM3, PM6, RM1 or MNDO.

• CI: Singles (CIS), Doubles, Singles + doubles (CISD) or Full CI.

• Active electrons and Active orbitals: the active space, centred on the HOMO/LUMO. Full CI grows combinatorially: keep the active space small.

• States: the number of states computed.

The reference SCF with fractional occupancy does not always converge (the job then fails with "SCF Converger error: Too many iterations"); in that case try the MOM tab.

MOM tab (with intensities)

The maximum overlap method (Gilbert, Besley and Gill, 2008) runs one SCF for each excited determinant (HOMO−o → LUMO+v, alpha spin, unrestricted), and computes the transition dipole and oscillator strength with pDynamo. Open-shell singlets are spin-mixed determinants.

• Method: a semi-empirical Hamiltonian (AM1, PM3, PM6, RM1, MNDO) or an ab initio/DFT level (HF/6-31G*, B3LYP/6-31G*, HF/def2-SVP, B3LYP/def2-SVP, PBE/def2-SVP).

• Excitations (o,v): the orbital swaps HOMO−o → LUMO+v, separated by ";" (default: 0,0; 0,1; 1,0; 1,1).

Results

The table lists, for each state, the excitation energy in eV and kJ/mol, the wavelength in nm and, for MOM, the oscillator strength (f) and the overlap with the ground state; the spectrum is plotted below the table (Figure 1). Export Table... saves the results.