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Charge distributions and chemical effects. XXXIV. Concepts involved in an approximate, but accurate, description of bond energies
Author(s) -
Fliszár Sándor
Publication year - 1984
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.560260514
Subject(s) - chemistry , bond energy , molecule , atom (system on chip) , charge (physics) , electron , simple (philosophy) , chemical bond , atoms in molecules , constant (computer programming) , computational chemistry , atomic physics , single bond , potential energy , quantum mechanics , physics , group (periodic table) , organic chemistry , philosophy , epistemology , computer science , programming language , embedded system
The concepts underlying the definition of bond energies in terms of potentials at the nuclei are outlined. The theory is rooted, first, in a definition of the energy, E i , of “atom” i in the molecule in terms of the potential energy, V ( i , mol), of nucleus Z i in the field of all the electrons and nuclei of the molecule: E i = K i molV ( i , mol). The K i molparameter, which is not required to be a constant in the derivation of the energy expression describing the contribution of an ij bond, turns out to be virtually constant for each atomic species—a situation which is exploited in numerical applications. Second, the Hellmann—Feynman theorem is applied in the calculation of the derivative, δΔ E a * /δ Z i , of the atomization energy, Δ E a * , using (i) the exact quantum‐chemical definition of Δ E a *and (ii) the view that Δ E a *is the sum of bond energy contributions, ε ij , plus a small interaction between nonbonded atoms. The individual bond energies derived in this manner necessarily depend on local charges at the bond‐forming atoms. Numerical applications illustrate how this new bond‐energy formula provides a simple link between typical saturated, olefinic, acetylenic, and aromatic hydrocarbons.