Multiwfn forum

Louischarlc0

Member

Registered: 2020-07-21

Posts: 65

intermolecular orbital overlap

Dear Prof Lu

I've calculated the intermolecular orbital overlap for my dimer compound. However, I'm not sure how to interpret the result as the manual does not explain it on page 774. For both HOMO-HOMO and LUMO-LUMO overlaps I got negative results. As I'm under the impression that orbital overlap is related to the strength of interaction between monomers, what does it mean to get negative or positive result and what does the value of the result say about the magnitude of the interaction?

Thanks in advance

Regards
Louis-Charl

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: intermolecular orbital overlap

Dear Louis-Charl

Because orbital wavefunction has phase, namely the value can be either positive or negative in different positions, certainly the integral of product of two orbitals wavefunctions may be negative.

If you only want to study degree of spatial overlap and the phase is not of interest, you should compute integral of product of norm of two orbitals wavefunctions, the result is always positive and proportional to degree of spatial overlap. This can be realized by the function described in Section 3.200.6 of Multiwfn manual, see below

In addition, it should be noted that orbital interaction usually doesn't play a major role in intermolecular interaction, therefore the overlap should not be overinterpreted. Also it is noteworthy that the ETS-NOCV analysis in Multiwfn is quite useful in studying interfragment orbital interaction, including intermolecular interaction, as illustrated in Section 4.23.4 of Multiwfn manual.

Best regards,

Tian

Louischarlc0

Member

Registered: 2020-07-21

Posts: 65

Re: intermolecular orbital overlap

Thank you for your response. However, I do not see section 4.23.4 in the latest version of the multiwfn manual. Are you sure it is not section 4.20.4 as it contains the info that you are describing.

Regards
Louis-Charl

Louischarlc0

Member

Registered: 2020-07-21

Posts: 65

Re: intermolecular orbital overlap

My apologies. I see you've updated the manual and found it page 816

Thank you

Regards
Louis-Charl