TY - JOUR

T1 - Parametric two-electron reduced-density-matrix method with application to diradical rectangular H4

AU - Sand, Andrew M.

AU - Mazziotti, David A.

PY - 2013/1/1

Y1 - 2013/1/1

N2 - 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.

AB - 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.

KW - Electron correlation

KW - Parametric method

KW - Potential energy curves

KW - Reduced density matrices

UR - http://www.scopus.com/inward/record.url?scp=84871789391&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84871789391&partnerID=8YFLogxK

U2 - 10.1016/j.comptc.2012.09.033

DO - 10.1016/j.comptc.2012.09.033

M3 - Article

AN - SCOPUS:84871789391

VL - 1003

SP - 44

EP - 49

JO - Computational and Theoretical Chemistry

JF - Computational and Theoretical Chemistry

SN - 2210-271X

ER -