Size extensivity of the variational reduced-density-matrix method
- Advanced Center for Computing and Communication, RIKEN, 2-1 Hirosawa, Wako City, Saitama 351-0198 (Japan)
With the density-matrix variational method, the ground-state energy of a many-electron system is calculated by minimizing the energy expectation value subject to the selected representability conditions for the second-order reduced-density matrix (2-RDM). There is a lack of size extensivity under the P, Q, and G conditions of this method by applying to M noninteracting atoms and molecules up to M=32; Be{sub M}, (CH{sub 4}){sub M}, and (N{sub 2}){sub M}. The energy per molecule (E/M) monotonically decreases as M increases, showing the lack of size extensivity in this method. The inextensive contributions to energies are 3x10{sup -4} and 3x10{sup -3} a.u. for (CH{sub 4}){sub M} and (N{sub 2}){sub M} using the STO-6G basis set, respectively. In the examples studied, E/M approaches a finite value as M{yields}{infinity}. The intermolecular elements of 2-RDMs do not satisfy the cumulant expansion.
- OSTI ID:
- 21316348
- Journal Information:
- Physical Review. A, Vol. 80, Issue 4; Other Information: DOI: 10.1103/PhysRevA.80.042109; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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