Local CC2 response method based on the Laplace transform: Orbital-relaxed first-order properties for excited states

Abstract

A pair natural orbital implementation of the coupled cluster model CC2 for excitation energies J. Chem. Phys. 139, 084114 (2013) A multistate local CC2 response method for the calculation of orbital-relaxed first order properties is presented for ground and electronically excited states. It enables the treatment of excited state properties including orbital relaxation for extended molecular systems and is a major step on the way towards analytic gradients with respect to nuclear displacements. The Laplace transform method is employed to partition the eigenvalue problem and the lambda equations, i.e., the doubles parts of these equations are inverted on-the-fly, leaving only the corresponding effective singles equations to be solved iteratively. Furthermore, the state specific local approximations are adaptive. Densityfitting is utilized to decompose the electron-repulsion integrals. The accuracy of the local approximation is tested and the efficiency of the new code is demonstrated on the example of an organic sensitizer for solar-cell applications, which consists of about 100 atoms. © 2013 AIP Publishing LLC. [http://dx

Oscillator strengths, first-order properties, and nuclear gradients for local ADC(2)

“…For excited states, the formalism for the LADC(2) orbital relaxed first-order properties is derived analogously as in Ref. 23. The central quantity here is the Lagrangian…”

“…[20][21][22][23][24] We therefore employ mutually orthogonal LMOs to span the occupied space, as obtained by Pipek-Mezey localization, 26 and non-orthogonal PAOs to span the virtual space. In the following, we employ indices i, j, .…”

“…Quite recently, we implemented, on that basis, also nuclear gradients. 23,24 With these, excited state geometry optimizations of pretty large molecular systems are possible at the CC2LR level.…”

“…[18][19][20][21][22][23][24] Local correlation methods exploit the relatively quick decay of dynamic correlation effects in non-metallic systems. To this end, spatially local orbitals are employed to span occupied and virtual space as specified by the underlying Hartree-Fock reference wave function, i.e., mutually orthogonal localized molecular orbitals (LMOs) and non-orthogonal projected atomic orbitals (PAOs), 25 where the former are obtained from a Pipek-Mezey localization 26 of the canonical occupied orbitals.…”

Periodic local MP2 method employing orbital specific virtuals

“…The PAO approach has been employed in molecular local MP2 [40][41][42][43][44] and coupled cluster [45][46][47][48][49][50][51][52] methods including explicit correlation, [53][54][55] in time-dependent coupled cluster linear response, [56][57][58][59][60] as well as in multireference techniques. 61 Also the periodic local MP2 26,[62][63][64] and MP2-F12 28 methods as implemented in the CRYSCOR program 26 so far employ PAOs.…”