Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation
Abstract
Generalized gradient approximations (GGA's) seek to improve upon the accuracy of the localspindensity (LSD) approximation in electronicstructure calculations. Perdew and Wang have developed a GGA based on realspace cutoff of the spurious longrange components of the secondorder gradient expansion for the exchangecorrelation hole. We have found that this density functional performs well in numerical tests for a variety of systems: (1) Total energies of 30 atoms are highly accurate. (2) Ionization energies and electron affinities are improved in a statistical sense, although significant interconfigurational and interterm errors remain. (3) Accurate atomization energies are found for seven hydrocarbon molecules, with a rms error per bond of 0.1 eV, compared with 0.7 eV for the LSD approximation and 2.4 eV for the HartreeFock approximation. (4) For atoms and molecules, there is a cancellation of error between density functionals for exchange and correlation, which is most striking whenever the HartreeFock result is furthest from experiment. (5) The surprising LSD underestimation of the lattice constants of Li and Na by 34 % is corrected, and the magnetic ground state of solid Fe is restored. (6) The work function, surface energy (neglecting the longrange contribution), and curvature energy of a metallic surface are all slightly reduced in comparison with LSD. Taking account of the positive longrange contribution, we find surface and curvature energies in good agreement with experimental or exact values. Finally, a way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects.
 Publication:

Physical Review B
 Pub Date:
 September 1992
 DOI:
 10.1103/PhysRevB.46.6671
 Bibcode:
 1992PhRvB..46.6671P
 Keywords:

 71.45.Gm;
 31.20.Sy;
 68.35.Md;
 71.45.Nt;
 Exchange correlation dielectric and magnetic response functions plasmons;
 Surface thermodynamics surface energies