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Degenerate density perturbation theory
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DOI：10.1103/PhysRevB.94.115108.png)
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Abstract
En 中文
Fractional occupation numbers can be used in density functional theory to create a symmetric Kohn-Sham potential, resulting in orbitals with degenerate eigenvalues. We develop the corresponding perturbation theory and apply it to a system of N-d degenerate electrons in a harmonic oscillator potential. The order-by-order expansions of both the fractional occupation numbers and unitary transformations within the degenerate subspace are determined by the requirement that a differentiable map exists connecting the initial and perturbed states. Using the X alpha exchange-correlation (XC) functional, we find an analytic solution for the first-order density and first-through third-order energies as a function of a, with and without a self-interaction correction. The fact that the XC Hessian is not positive definite plays an important role in the behavior of the occupation numbers.
Keywords:
GROUND-STATE ENERGIES
FUNCTIONAL THEORY
SYSTEMS
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