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Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,622

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Is there anything interesting in the UV-Vis spectrum analysis?

Recently a ResearchGate user asked a question about how to perform advanced and interesting electronic excitation analysis, his question:
https://www.researchgate.net/post/Is_th … l_analysis

Title:Is there anything interesting in the UV-Vis spectrum (excluding energy transition, Wavelength max, homo-lumo) for molecular structural analysis?

I like to include anything novel approach in the my research write up. I wanna try anything different approach from prototypical old approach. Please give me some suggestions.

My reply

If you meant you want to add some advanced or novel analyses for studying electronic excitation problem, there are some methods you may consider, all of them can be easily realized via Multiwfn in combination with a popular quantum chemistry code such as Gaussian and ORCA. Multiwfn is freely available at http://sobereva.com/multiwfn

(1) Density difference map between excited state and ground state: This analysis helps you to understand electronic structure reorganization during electronic transition. This can be easily done using Multiwfn, see Section 4.5.5 of Multiwfn manual for example
(2) Transition density matrix map: This enable you to immediately capture the main molecular region involved in the transition and investigate coupling between various atoms. See Section 4.18.2 of Multiwfn manual for example.
(3) Interfragment charge transfer analysis: This analysis describes amount of electron transferation between two arbitrarily defined molecular fragments. See Section 4.18.6 of Multiwfn manual for example.
(4) Analysis of transition dipole moment contributed by various molecular fragments: Oscillator strength is positively proportional to transition dipole moment, which is possible to be decomposed to molecular fragment contributions. Clearly this analysis helps you understanding how various fragments affect strength of spectrum peak. See Section 4.18.5 of Multiwfn manual for example.
(5) hole-electron analysis: This is a powerful module of Multiwfn program, it can calculate hole and electron distribution (electronic excitation can be represented as hole->electron transition), and based on them, charge transfer distance (i.e. distance between centroid of hole and electron) and overlap between hole and electron can be calculated, and then used to identify type of electronic excitation. Atomic contribution to hole and electron can also be quantified. Besides, Coulomb attractive energy between hole and electron can be evaluated. Furthermore, this module can draw transition dipole moment map, so that contribution to transition dipole moment from every position in 3D space can be vividly examined.
(6) Natural transition orbitals (NTO) analysis: This is a very popular analysis method, it is quite useful when you need to study orbital transition but there is no unique dominating molecular orbital pair. See Section 4.18.4 of Multiwfn manual for example.
(7) Population analysis: By comparing electronic population on atoms or atomic orbitals between ground and excited states, you can make clear how charge transfer occur at the atomic or atomic orbital scale. Example of population analysis can be found in Section 4.7 of Muliwfn manual.
(8) Plotting contribution to spectrum of individual transitions. The spectrum plotting module of Multiwfn enables the overall spectrum be decomposed to individual contribution from various electronic transition, so that the underlying character of overall spectrum can be more clearly understood. See Section 4.11.2 of Multiwfn manual for example.

There are also many other functions in Multiwfn that closely related to electronic excitation problem, such as TrEsp(transition charge from electrostatic potential), ghost-hunter index, delta-r index, orbital overlap analysis. Theoretical introductions as well as examples can be found in the manual.