Potential Surface of H₂ - RHF, UHF, MP2, MP3 and MP4SDTQ -

Abstract

It is well known that UHF, UMP2, UMP3 and UMP4SDTQ can properly reproduce the potential surface of H₂ dissociation (H₂®H + H) whereas RHF, RMP2, RMP3, RMP4SDTQ do not easily reproduce the proper potential surface. In this note, we demonstrate this fact because there are few textbook qualitatively representing both of them. The difference of RHF and UHF is very small in region R_H-H<1.2Å and increases along with the increasing of R_H-H>1.2Å. Corresponding to this trend, the electron correlation is large in the region R_H-H<1.2Å but rapidly decreases along with increasing of R_H-H. Finally the electron correlation is almost 0 in region R_H-H>2.0Å.