J. Phys. Chem. 1996, 100, 6167-6172
6167
Refinement of the Asymptotic Z Expansion for the Ground-State Correlation Energies of Atomic Ions Subhas J. Chakravorty and Ernest R. Davidson* Department of Chemistry, Indiana UniVersity, Bloomington, Indiana 47405 ReceiVed: September 20, 1995; In Final Form: December 7, 1995X
Davidson and co-workers (Phys. ReV. A 1991, 44, 7071; 1993, 47, 3649) have estimated the nonrelativistic correlation energies and relativistic corrections to ionization potentials for atomic ions with up to 18 electrons. However, due to the lack of theoretical values for the high-Z limits and lack of more accurate compilations of experimental ionization potentials, the analysis for 11-18 electrons required further investigation. In this work, we have accurately determined the exact high-Z limit employing degenerate second order perturbation theory for the correlation contribution to the energies of atomic ions with 3-18 electrons. We have also incorporated the experimental compilation of the electron affinity data of Hotop and Lineberger for the low-Z limit. This high-Z limit is compared with the results of the LYP correlation energy functional. The LYP correlation functional is also compared with the correlation energy of electrons in an external harmonic potential of infinite force constant.
Atomic Correlation Energies Accurate and dependable compilations of nonrelativistic atomic correlation and total energies provide a useful guideline for the development of more sophisticated models used in electronic structure calculations. In two recent papers, Davidson and co-workers1-2 have estimated the exact ground-state correlation energies Ec(N,Z) of hypothetical nonrelativistic atomic ions with N electrons and nuclear charge Z, for N up to 18 electrons. However, due to lack of theoretical high-Z limits for the correlation energy, the previous study could not make a definitive estimate of the correlation energy for high-Z ions for N ) 11 to N ) 18. To understand the theoretical development of the present work, we retrace some of the essential steps presented in our earlier studies. The total nonrelativistic, stationary-point-nucleus energy, E(N,Z) is defined as the exact ground-state eigenvalue of the Hamiltonian defined as (in atomic units) N
N
i)1
j
