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There is also possible to perform quenching of the excited state. The example is shown on the above mentioned system. CH2=N2 molecule can be found in two symetric conformations (Hydrogen bounded on N is in left or on the right side). Such transition is carried out by excitation of one electron from Homo to Lumo. Transition from one conformation to another pass through the conical intersection which is the local minimum of the excited state. In this example we will optimize geometry to the conical intersection. We only switch on keyword iquench = 1 and let them relax. Example of fireball in is below and elh.in file is the same as above:
&OPTION basisfile = CNH3.bas icluster = 1 nstepf = 5000 T_initial = 100.0 T_final = 100.0 sigmatol = 0.00000001 dt = 0.5 iquench = 1 max_scf_iterations = 200 iscfe = 1 &END &OUTPUT iwrteigen = 1 iwrtxyz = 1 &END &MESH &END