Calculation of excitation energies: *EXCITA

 

Directives to control the calculations of electronic transition  properties and excitation energies  appear in the *EXCITA input module. For SCF    wave functions the properties are calculated using the random phase approximation (RPA) and for MCSCF  wave functions the multiconfigurational (MC)-RPA is used. Implemented electronic transition properties are at the moment:

1. Oscillator Strength  which determines visible and UV absorption.
2. Rotatory Strength  which determines Electronic Circular Dichroism   (ECD).
3. Excitation Energies  . These are always calculated when invoking the .EXCITA keyword in the general input module.

.DIPSTR Calculates the dipole strength , that is, the dipole oscillator strength which determine the visible and UV absorption, using the dipole length form.

.FNAC Calculate first-order non-adiabatic coupling matrix  elements. This is not yet fully implemented in the ABACUS  program package and must be combined with subsequent RESPONSE-calculations.

.IPRINT
READ (LUCMD, *) IPRINT

Set the print level in the calculation of the necessary differentiated integrals when calculating the linear response functions. Read one more line containing print level. Default value is the value of IPRDEF from the general input module. The print level of the rest of the calculation of electronic excitation energies are controled by the keyword .PRINT .

.MAXITE
READ (LUCMD,*) MAXITE

Set the maximum number of micro iterations in the iterative solution of the linear response equations. Read one more line containing maximum number of micro iterations. Default value is 40.

.MAXPHP
READ (LUCMD,*) MXPHP

Set the maximum dimension for the sub-block of the configuration Hessian that will be explicitly inverted. Read one more line containing maximum dimension. Default value is 0.

.MAXRED
READ (LUCMD,*) MXRM

Set the maximum dimension of the reduced space to which new basis vectors are added as described in Ref. [7]. Read one more line containing maximum dimension. Default value is 400.

.NEXCIT
READ (LUCMD, '(8I5)') (NEXCIT(I), I= 1,8)

Set the number of excitation energies  to be calculated in each symmetry. Read one more line containing the number of excitations in each of the irreducible representations of the molecular point group. The default is not to calculate any excitation energies in any of the irreducible representations.

.OPTORB Use optimal orbital trial vectors  in the iterative solution of the frequency dependent linear response  equations. These are generate by solving the orbital response equation exact, keeping the configuration part fixed as described in Ref. [7].

.PRINT
READ (LUCMD,*) IPREXE

Set the print level in the calculation of electronic excitation energies. Read one more line containing the print level. The default value is the IPRDEF from the general input module.

.ROTVEL Calculate rotational strengths   in Electronic Circular Dichroism (ECD) without using London orbitals.

.SKIP Skip the calculation of electronic excitation energies. This will give wrong results for ECD and first-order NACMEs. Mainly for debugging purposes.

.STOP Stops the program after finishing the calculation of the linear response functions. Mainly for debugging purposes.

.THREXC
READ (LUCMD,*) THREXC

Set the convergence threshold for the solution of the linear response equations. Read one more line containing the convergence threshold. The default value is .

.TRIPLE  

Indicates that it is triplet excitations  that is to be investigated.