Journal Article: Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

Title: Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ω{sub α} and oscillator strengths f{sub α} for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bondmore » in the field of occupied (including core) orbitals. ELS(1) produces high quality ω{sub α}(R) curves along the bond dissociation coordinate R for the molecules LiH, Li{sub 2}, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate.« less

Faculty of Exact Sciences, Theoretical Chemistry, VU University, Amsterdam (Netherlands)

(Korea, Republic of)

(Saudi Arabia)

Publication Date:

OSTI Identifier:

22253629

Resource Type:

Journal Article

Resource Relation:

Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 2; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CURRENT DENSITY; DENSITY MATRIX; DISSOCIATION; ELECTRON PAIRS; ELECTRONS; EXCITATION; GROUND STATES; OSCILLATOR STRENGTHS; RESPONSE FUNCTIONS; TIME DEPENDENCE; WAVE FUNCTIONS