Parameterization of the two-electron reduced density matrix (2-RDM) has made possible the determination of electronic energies with greater accuracy and reduced computational cost compared to traditional electron-pair theories, including coupled cluster with single and double excitations [D.A. Mazziotti, Phys. Rev. Lett. 101 (2008) 253002]. We apply the method to an H4 model system, a rectangular arrangement of two H2 monomers (P4), which is often used for benchmark calculations of multireference methods. At the square geometry, H4 becomes a diradical. We find that the parametric 2-RDM method obtains occupation numbers of 0.5471 and 0.4489 for the Nth and (N+1)th natural orbitals, respectively, which indicate diradical character. Energies and orbital occupation numbers obtained from the parametric 2-RDM method are found to be more accurate than single-reference wavefunction methods of comparable computational cost. We report energies and natural orbital occupation numbers for several geometries in the rectangular H4 system.
|Original language||English (US)|
|Number of pages||6|
|Journal||Computational and Theoretical Chemistry|
|State||Published - Jan 1 2013|
Bibliographical noteFunding Information:
D.A.M. gratefully acknowledges the NSF, the ARO, the Henry-Camille Dreyfus Foundation, the David-Lucile Packard Foundation, the Keck Foundation, and the Microsoft Corporation for their support.
Copyright 2013 Elsevier B.V., All rights reserved.
- Electron correlation
- Parametric method
- Potential energy curves
- Reduced density matrices