Orbital forces and chemical bonding in density-functional theory: Application to first-row dimers
The local-density-functional description of chemical bonding in first-row homonuclear dimers is analyzed in terms of both static and dynamic orbital forces. The dynamic orbital force of the i-italicth molecular orbital is equal to the negative of the derivative of the one-electron energy epsilon-c/sub i-italic/ with respect to the p-italicth nuclear coordinate, i.e., -partialepsilon-c/sub i-italic//partialX/sub p/. The static orbital force is also equal to a derivative of the one-electron energy, but the differentiation is carried out with the orbital held fixed, i.e., (-partialepsilon-c/sub i-italic//partialX/sub p/)psi. It is shown that the static force is the orbital's contribution to the total Hellmann-Feynman force, whereas the dynamic force describes the change in the total force due to change in the orbital's occupation number. The chemical bond force in the first-row dimers is observed to be a delicate balance between bonding and antibonding orbital forces. Most of the bond force comes from the 2sigma/sub g-italic/ orbital and to a lesser extent from the 1..pi../sub u-italic/ state. The polarization of the core orbitals in N/sub 2/, O/sub 2/, and F/sub 2/ is found to originate indirectly through their interaction with the 3sigma/sub g-italic/ orbital. The dynamic orbital force gives accurate predictions about the change of equilibrium bond distances accompanying electronic ionization and excitation. The formalism and results are related to earlier Hartree-Fock studies.
- Research Organization:
- Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, Tennessee 37831
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5380704
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Vol. 34:4
- Country of Publication:
- United States
- Language:
- English
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