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http://hdl.handle.net/11154/1622
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Title: | On the restricted and combined use of Rudenberg's approximations in molecular orbital theories of Hartree-Fock type |
Authors: | Koch, W Frey, B Ruiz, JFS Scior, T |
Issue Date: | 2003 |
Abstract: | Rudenberg's well-known letter of 1951 entitled "On the Three- and Four-Center Integrals in Molecular Quantum Mechanics" explicitly presents two approximation formulas for four-center repulsion integrals, only. When applied to some types of three-center repulsion integrals, however, these two recipes still imply considerable oversimplifications. Using both one-electron and two-electron routes of Rudenberg's truncated expansion, on the other hand, such shortcomings can be avoided strictly. Starting from four simple "Unrestricted and Combined" (U&C) approximation schemes introduced elsewhere, an improved "Restricted and Combined" (R&C) approximation picture for Fock-matrix elements now will be outlined, which does not tolerate any unnecessary oversimplifications. Although the simplicity of the U&C scheme is lost in this case, R&C-approximated Fock-matrix elements still can be constructed from one- and two-center integrals alone in an effective way. Moreover, due to their dependence on a single geometric parameter, all types of two-center integrals can be calculated in advance for about one hundred fixed interatomic distances at the desired level of sophistication and stored once and for all. A cubic spline algorithm may be taken to interpolate the actual integral value from each precomputed list. |
URI: | http://hdl.handle.net/11154/1622 |
ISSN: | 0932-0784 |
Appears in Collections: | Ciencias
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