Etsecs
From cclib
The singly-excited configurations that contribute to electronic transitions are stored in etsecs. It is a list (for each electronic transition from the reference ground state) of lists (for each singly-excited configuration) with three members each:
- a tuple (moindex, alpha/beta), which indicates the MO where the transition begins
- a tuple (moindex, alpha/beta), which indicates the MO where the transition ends
- a float (which can be negative), the coefficient of this singly-excited configuration
In these tuples, the value of alpha/beta is 0 or 1, respectively. For a restricted calculation, this value is always 0, although some programs (GAMESS) sometimes print coefficients for both alpha and beta electrons.
The excitation coefficient is always converted to its unnormalized value by cclib - so the sum of the squared coefficients of all alpha and beta excitations should be unity. It is important to keep in mind, however, that only the square of the excitation coefficient has a physical meaning, and its sign depends on the numerical procedures used by each program.
Availability
- Configuration Interaction (CIS): Gaussian
- Time-dependent DFT (TD-DFT): Gaussian
- Time-dependent Hartree-Fock (TD-HF): Gaussian
Availability (development version)
- Configuration Interaction (CIS): GAMESS, Gaussian, Jaguar
- Time-dependent DFT (TD-DFT): GAMESS, Gaussian
- Time-dependent Hartree-Fock (TD-HF): Gaussian
