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Introduction to Solid State theory, DFT and the APW-method - WIEN 2k

Introduction to Solid State theory, DFT and the APW-method - WIEN 2k

Introduction to Solid State theory, DFT and the APW-method - WIEN 2k

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Exchange <strong>and</strong> correlation• We divide <strong>the</strong> density of <strong>the</strong> N-1 electron systemin<strong>to</strong> <strong>the</strong> <strong>to</strong>tal density n(r) <strong>and</strong> an exchangecorrelationhole:Properties of <strong>the</strong> exchange-correlation hole:• Locality• Pauli principle• <strong>the</strong> hole contains ONE electron• The hole must ne negative• The exchange hole affects electrons with <strong>the</strong>same spin <strong>and</strong> accounts for <strong>the</strong> Pauli principle• In contrast, <strong>the</strong> correlation-hole accounts for <strong>the</strong>Coulomb repulsion of electrons with <strong>the</strong> oppositespin. It is short range <strong>and</strong> leads <strong>to</strong> a smallredistribution of charge. The correlation holecontains NO charge:

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