Hi developers and users,
I hope you can assist me with a question. I have been attempting to perform Constrained DFT optimization combined with PCM calculations. While the optimization seems successful, I have noticed an unexpected result when proceeding to TDDFT calculations. The CT state excitation energy appears higher compared to the results obtained in vacuum.
I would greatly appreciate any guidance or insight you can offer to help me understand and address this discrepancy. Thank you in advance for your time and expertise.
This is not so unexpected as it may seem at first. It is entirely possible for the dipole moment to be smaller in the excited state than it is in the ground state, in which situation it is the ground state that is more stabilized than the excited state, which in turn leads to increased excitation energy in the polar solvent with respect to a non polar one (or vacuum). This may even happen if the excited state - the direction of the electron transfer must just largely coincide with the direction of the ground state dipole moment.