Multiwfn forum

I have recently run ORCA SPE calculations, MP2/cc-pVTZ(-f), on the ion dimethylimidazolium that has been geometry optimized using RHF/6-31G(d). I wanted to use the output to calculate the CHELPG charges on the atoms. ORCA has a built-in CHELPG routine which I initially used, but it gave suspect results (not consistent with some literature values, and some charges too large). I then ran the ORCA wavefunction output through Multiwfn, and got significantly different CHELPG charges than what ORCA produced, (but closer to the literature and more physically reasonable). Both Multiwfn and ORCA CHELPG calculations were done under identical parameters (vdw radii, cutoff length, grid density). See data below. Clearly, there is a discrepancy in how ORCA and Multiwfn determine the CHELPG charges for the same ORCA output. Given the greater difference between the ORCA CHELPG calculations and the literature values, I assume there is an problem with the way ORCA is calculating the CHELPG charges, but I don't know that for sure. I do not have Gaussian or GAMESS or another electronic structure package to compare additional CHELPG routines.

I am posting this to see if anyone else has had experience with discrepancies like this between different CHELPG routines?

Atom    ORCA CHELPG     Multiwfn CHELPG          DOI: 10.1021/jp0362133             DOI: 10.1016/j.molliq.2015.03.040 (in Supplementary Info)
NA             0.278                     0.147                          0.152                                              0.146
CR            -0.141                    -0.047                         -0.106                                     -0.046
NA             0.282                     0.136                          0.153                                              0.146
CW            -0.244                    -0.152                         -0.127                                     -0.135
CW            -0.242                    -0.173                         -0.127                                     -0.135
C1            -0.422                    -0.191                         -0.174                                     -0.177
HCR     0.243                     0.222                          0.206                                              0.202
C1            -0.426                    -0.177                         -0.173                                     -0.177
HWR     0.263                     0.222                          0.205                                              0.202
HWR     0.263                     0.228                          0.205                                              0.192
H1            0.192                     0.128                          0.131                                              0.125
H1            0.188                     0.135                          0.131                                              0.125
H1            0.192                     0.135                          0.131                                              0.142
H1            0.193                     0.126                          0.131                                              0.142
H1            0.188                     0.131                          0.131                                              0.125
H1            0.193                     0.131                          0.131                                              0.125

Finally, there are some errors in documentation out there for the CHELPG procedure. According to the original paper (DOI: 10.1002/jcc.540110311), the grid spacing is 0.3 Angstroms and the cut-off length is 2.8 Angstroms. Occasionally, these get converted, INCORRECTLY, to 3 pm and 28 pm. (See https://www.cup.uni-muenchen.de/ch/comp … lpg.html.) This unit conversion error is also present on page 72 of the Multiwfn 3.6 manual (and presumably other versions). Perhaps some of the issues I've seen in inconsistent results between different CHELPG routines are due to some conversion errors?

Any insight here from anyone would be appreciated. Thanks.