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He 2+ 2 : A comparison between Hartree–Fock and density functional techniques
Author(s) -
Ventura Oscar N.,
Bartolucci J. Paolo,
Sosa Ramón M.
Publication year - 1985
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560270511
Subject(s) - linear combination of atomic orbitals , symmetry (geometry) , hartree–fock method , chemistry , space (punctuation) , energy (signal processing) , atomic physics , quantum mechanics , density functional theory , physics , computational chemistry , mathematics , computer science , geometry , basis set , operating system
Abstract A comparison of Roothaan‐Hartree–Fock methods (both restricted and unrestricted) with density functional ones ( LCAO ‐ X α and cellular MS ‐ X αβ) is made using as test case the He 2 2 + molecular ion. It is shown the analogy that exists between RHF and symmetry‐adapted LCAO ‐ X α potential energy curves, as well as between UHF and symmetry‐unconstrained LCAO ‐ X α ones. The influence of symmetry adaptation on the overall behavior of the potential energy curve is also discussed. Finally, the difference in the behavior of the LCAO ‐ X α and cellular MS ‐ X αβ calculations is explained as an artifact of the space partitioning in the latter technique. It is concluded that LCAO ‐ X α method is superior to cellular MS ‐ X αβ because it requires less effort to reach the same results and that the general behavior is similar to UHF , although the former affords a better equilibrium bond distance and a worse energy barrier than the latter.