Multiwfn forum / Determination of crucial excited state for two-level model

Re: Determination of crucial excited state for two-level model

dummy@example.com (sobereva) — Mon, 10 Feb 2020 23:59:59 +0000

If your system shows single direction CT character, such as the K3O-Si12C12 cluster studied in my J. Comput. Chem., 38, 1574 (2017) paper, you should reorientate the system so that the CT direction corresponds to one of Cartesian axis. (Do not forget to add "nosymm" keyword in the calculation)

Re: Determination of crucial excited state for two-level model

dummy@example.com (fyzan) — Mon, 10 Feb 2020 07:59:45 +0000

Sir to properly orient should we orient dipole moment of the molecule along Z axis to get significant component of beta as betaZZZ?

Re: Determination of crucial excited state for two-level model

dummy@example.com (sobereva) — Mon, 10 Feb 2020 06:00:29 +0000

The two statements are equivalent, because the oscillator strength is proportional to square of norm of transition dipole moment.

If you only want to use two-level model to analyze BetaXXX to unveil its major source, you should determine crucial excited state according to X component of transition dipole moment (rather than norm of transition dipole moment).

PS: Commonly, you should properly orientate your system so that the largest component of beta just corresponds to one of Cartesian axes. For example, in my J. Comput. Chem., 38, 1574 (2017) paper, the only significant component of beta is betaZZZ. Although I used oscillator strengh to determine the crucial state, in this case the conclusion is identical to using Z component of transition dipole moment to determine crucial state.

Both the two variations of dipole moment are meaningful, the first one is calculated based on unrelaxed density of excited state, while the latter one corresponds to relaxed density of excited state. In principle, the later one is more real, however if you intend to perform two-level analysis, you have to use the former one, because its definition is compatible with the two-level formula.

Determination of crucial excited state for two-level model

dummy@example.com (fyzan) — Mon, 10 Feb 2020 05:09:57 +0000

Hi Dear professor Lu, in your work J. Comput. Chem., 38, 1574 (2017) it is reported that crucial excited state corresponds to the lowest-lying one with large oscillator strength, whereas in Multiwfn manual "4.200.8.2 Perform two- and three-level model analysis for first
hyperpolarizability of NH2-biphenyl-NO2" excited state with larger magnitude of "Tot" (norm of transition dipole moment) is considered as crucial excited state. Are these two statements always results in same excited state? if they corresponds to different states then which one to prefer?
if we are considering BetaXXX and excited state having highest Tot" (norm of transition dipole moment) has low transition dipole component in X direction as compared to another state having low Tot" (norm of transition dipole moment) but higher transition dipole component then which state should be considered crucial excited state?

another confusion i have is that "Variation of dipole moment component" outputted by Multiwfn should be reported or the Variation of dipole moment calculated by finding difference in ground state and excited state with density=current keyword in gaussian?

thanks