Yes, you are quite right.
Using "density=current" leads both SCF and MP2 densities to be saved in the "chk" file which could simply viewed when "chk" is converted into a readable format such as "fch". But, if such "chk" file is directly loaded into Multiwfn, only SCF density is taken into account for AIM analysis. Consequently, to avoid an additional calculation (out=wfn, density=current leading to wavefunction file with MP2 density, the procedure) recommended by Tian is the best and perfect.

Saeed

Only when "density" (equivalent to density=current) is added, density matrix of MP2 level will be generated and saved into .chk file. So it impacts.

Dear Tian,
Thank you very very much, my nice friend for your highly professional comments I have never been encountered with.

It seems, including or not including "density=current" in the Gaussian input file have not any impact. Indeed, after finishing a (for instance) opt+freq computation using MP2, the generated "chk" file must be converted into "fch" and then follow your instruction.

Sincerely,
Saeed

Dear Saeed,

After loading the .fch file produced by "MP2 density" calculation, input
200
16
MP2
y

Then the subsequent analysis result will correspond to MP2 level, and at the meantime, the new.mwfn generated in the current folder records natural orbitals at MP2 level, in the future you can also directly perform analysis at MP2 level using this file as input file.

Best,

Tian

Dear Tian,

I have optimized a molecular structure using "MP2/genecp". Then, corresponding ".chk" file was loaded into Multiwfn to compute QTAIM descriptors at desirable BCP in the hope that the MP2 density is considered by Multiwfn. But, it seems SCF density has been used to perform QTAIM analysis.
As I checked, I have to prepare "wfn" file using "density=current" keyword to reach the goal mentioned.
Please, if possible, let me know if there is another way to force Multiwfn considers MP2 density when I load "chk" file in that and, I have not to perform an additional calculation for generating "wfn" file.

Sincerely,
Saeed