Multiwfn forum

keelanb

Member

Registered: 2023-08-08

Posts: 2

ELF Analysis at the MP2 and Coupled Cluster Level

Hello,

I have a question regarding carrying out ELF analysis at the MP2 or coupled cluster level of theory. According to the linked paper (https://doi.org/10.1063/1.2210473), coupled cluster and MP2 do not fulfull the Hellmann-Feynman theorem. Therefore, the density or the pair density cannot be obtained as an expectation value. Does this mean that the results from ELF analysis on these wavefunctions are not as trustworthy, in a practical sense ? I have found that there is excellent agreement between the ELF analysis results at the CCSDT and ICE-CI (approximate full CI using ORCA), with regards to the ELF isosurface, and also the electron population of the integrated basins.

Thank you.

Keelan

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: ELF Analysis at the MP2 and Coupled Cluster Level

Dear Keelan,

According to kinetic energy density interpretation of ELF by Savin, ELF can also be calculated at MP2 and CCSD levels in terms of natural orbitals. This point has been mentioned in "9 Electron localization function (ELF)" of Section 2.6 of latest version of Multiwfn manual.

Best,

Tian

keelanb

Member

Registered: 2023-08-08

Posts: 2

Re: ELF Analysis at the MP2 and Coupled Cluster Level

Dear Tian,

Okay, thank you for your help.

Best,

Keelan