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Molecular binding in free space and in cold dense plasmas
Author(s) -
March N. H.
Publication year - 1990
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.560382460
Subject(s) - homonuclear molecule , density functional theory , diatomic molecule , potential energy , midpoint , density gradient , superposition principle , physics , chemistry , atomic physics , quantum mechanics , molecule , geometry , mathematics
The theory of the potential energy curve of dimers Na 2 and Be 2 embedded in a cold dense plasma is first developed, starting from linear response theory plus a low‐order gradient expansion. The results of this treatment are then reinterpreted, following the proposal of Perrot and March, in terms of bond midpoint properties. By comparison with full nonlocal density functional theory, the merits, and the limitations, of low‐order gradient expansions are then assessed for Na 2 and Be 2 in dense plasmas. Use is made in this discussion of a pair potential extracted by inversion of the measured structure factor for liquid Na just above its freezing point. There is truly excellent agreement with the full density functional treatment of Perrot and March. The question is then addressed as to the relevance of the characterization by bond midpoint properties of the potential energy curve for dimers in a dense plasma to free space diatomic molecules and molecular ions. For H 2 + , it is demonstrated that such a characterization is exact. Heavier homonuclear diatoms are then considered, withi a low‐order density gradient framework. It is emphasized that bond midpoint properties can again be used to characterize the potential energy curve. However, to obtain the electron density and its derivatives at the bond midpoint, it is now essential to solve the two‐center problem in free space diatomics, whereas for Na 2 and Be 2 in sufficiently dense plasmas the superposition of one‐center densities is an adequate starting point within the density functional framework.