The "JK-only" approximation in density matrix functional and wave function theory |
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Authors: | Kollmar Christian |
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Institution: | Lehrstuhl für Theoretische Chemie, Universit?t Erlangen, Egerlandstrasse 3, D-91058 Erlangen, Germany. christian.kollmar@chemie.uni-erlangen.de |
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Abstract: | Various energy functionals applying the "JK-only" approximation which leads to two-index two-electron integrals instead of four-index two-electron integrals in the electron-electron interaction term of the electronic energy are presented. Numerical results of multiconfiguration self-consistent field calculations for the best possible "JK-only" wave function are compared to those obtained from the pair excitation multiconfiguration self-consistent (PEMCSCF) method and two versions of density matrix functional theory. One of these is derived making explicit use of some necessary conditions for N representability of the second-order density matrix. It is shown that this method models the energy functional based on the best possible "JK-only" wave function with good accuracy. The calculations also indicate that only a minor fraction of the total correlation energy is incorporated by "JK-only" approaches for larger molecules. |
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