Ensemble v-representable ab initio density-functional calculation of energy and spin in atoms: A test of exchange-correlation approximations
- Raymond and Beverley Sackler Faculty of Exact Sciences, School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel) and Physics Department, Nuclear Research Center Negev, P. O. Box 9001, Beer Sheva 84190 (Israel)
The total energies and the spin states for atoms and their first ions with Z=1-86 are calculated within the the local spin-density approximation (LSDA) and the generalized-gradient approximation (GGA) to the exchange-correlation (xc) energy in density-functional theory. Atoms and ions for which the ground-state density is not pure-state v-representable are treated as ensemble v-representable with fractional occupations of the Kohn-Sham system. A recently developed algorithm which searches over ensemble v-representable densities [E. Kraisler et al., Phys. Rev. A 80, 032115 (2009)] is employed in calculations. It is found that for many atoms, the ionization energies obtained with the GGA are only modestly improved with respect to experimental data, as compared to the LSDA. However, even in those groups of atoms where the improvement is systematic, there remains a non-negligible difference with respect to the experiment. The ab initio electronic configuration in the Kohn-Sham reference system does not always equal the configuration obtained from the spectroscopic term within the independent-electron approximation. It was shown that use of the latter configuration can prevent the energy-minimization process from converging to the global minimum, e.g., in lanthanides. The spin values calculated ab initio fit the experiment for most atoms and are almost unaffected by the choice of the xc functional. Among the systems with incorrectly obtained spin, there exist some cases (e.g., V, Pt) for which the result is found to be stable with respect to small variations in the xc approximation. These findings suggest a necessity for a significant modification of the exchange-correlation functional, probably of a nonlocal nature, to accurately describe such systems.
- OSTI ID:
- 21450769
- Journal Information:
- Physical Review. A, Vol. 82, Issue 4; Other Information: DOI: 10.1103/PhysRevA.82.042516; (c) 2010 The American Physical Society; ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALGORITHMS
APPROXIMATIONS
ATOMS
CORRELATIONS
DENSITY FUNCTIONAL METHOD
ELECTRONIC STRUCTURE
ELECTRONS
ENERGY-LEVEL DENSITY
IONIZATION
IONS
RARE EARTHS
SPIN
ANGULAR MOMENTUM
CALCULATION METHODS
CHARGED PARTICLES
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
LEPTONS
MATHEMATICAL LOGIC
METALS
PARTICLE PROPERTIES
VARIATIONAL METHODS