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. In the case of Kohn-Sham DFT, time-dependent linear response theory is used in the adiabatic approximation with the exact functional kernel. 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.

.INTPRI

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 .

.MAX IT

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 60.

.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. [21]. READ ONE MORE LINE CONTAINING MAXIMUM DIMENSION. DEFAULT VALUE IS 400.

.NEXCIT

READ (LUCMD,*) (NEXCIT(I), I= 1,NSYM)

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 EIGENVALUE EQUATIONS. THESE ARE GENERATE BY SOLVING THE ORBITAL RESPONSE EQUATION EXACT, KEEPING THE CONFIGURATION PART FIXED AS DESCRIBED IN REF. [21].

.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. MAINLY FOR DEBUGGING PURPOSES.

.STOP

STOPS THE PROGRAM AFTER FINISHING THE CALCULATION OF THE EIGENVALUE EQUATIONS. MAINLY FOR DEBUGGING PURPOSES.

.SUMRUL

CALCULATE OSCILLATOR STRENGTH SUM RULES.

.THRESH

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 EXCITATION ENERGIES THAT IS TO BE CALCULATED.