DUGi

Benchmark calculations on the lowest-energy singlet, triplet, and quintet states of the four-electron harmonium atom

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@320721

For a wide range of confinement strengths ω, explicitly-correlated calculations afford approximate energies E(ω) of the ground and low-lying excited states of the four-electron harmonium atom that are within few μhartree of the exact values, the errors in the respective energy components being only slightly higher. This level of accuracy constitutes an improvement of several orders of magnitude over the previously published data, establishing a set of benchmarks for stringent calibration and testing of approximate electronic structure methods. Its usefulness is further enhanced by the construction of differentiable approximants that allow for accurate computation of E(ω) and its components for arbitrary values of ω. The diversity of the electronic states in question, which involve both single- and multideterminantal first-order wavefunctions, and the availability of the relevant natural spinorbitals and their occupation numbers make the present results particularly useful in research on approximate density-matrix functionals. The four-electron harmonium atom is found to possess the 3P+ triplet ground state at strong confinements and the 5S- quintet ground state at the weak ones, the energy crossing occurring at ω ≈ 0.0240919

The research described in this publication has been funded by NCN (Poland) under Grant No. DEC-2012/07/B/ST4/00553. The calculations have been carried out at the Wroclaw Center for Networking and Supercomputing (http://www.wcss.wroc.pl) and on the MareNostrum supercomputer of the Barcelona Supercomputing Center. The authors acknowledge computer resources, technical expertise, and assistance provided by the staff of the latter institution. In addition, one of the authors (E. M.) acknowledges financial support from the Career Integration Grant (Grant Agreement No. PCIG09-GA-2011-294240) and the Spanish MINECO (Project No. CTQ2013-41236-ERC)

American Institute of Physics (AIP)