Excited State Geometry Optimizations

The input for computing excited state gradients and properties using egrad is exactly the same as for an excited state calculation using escf, see the previous section. Gradients and properties are calculated only for one state at a time. By default, this is the highest excitation specified by $soes (only one IRREP is allowed). Sometimes, e.g. close to excited state intersections, it may be necessary to include higher excited states in the initial excitation vector calculation to prevent root flipping. This is accomplished using

$exopt n

which explicitly enforces treatment of the n-th state; n must be less or equal the number of states specified in $soes.

After the input for the ground and excited state calculations has been set up, an excited state geometry optimization can be started by issuing the command

nohup jobex -ex &

The option -ex forces jobex to call egrad instead of grad (or rdgrad if -ri is also specified). In each geometry step, the excitation energy is written on the fourth column in $energy, and the data group $last excitation energy change is updated. Otherwise, the excited state optimization proceeds in exactly the same way as a ground state optimization (see Chapter 3.1).