An efficient polarization propagator approach to valence electron excitation spectra

Abstract

A practical polarization propagator method devised for the treatment of valence electron excitations in atoms and molecules is presented. This method, referred to as (second-order) algebraic-diagrammatic construction (ADC(2)), allows for a theoretical description of single and double excitations consistently through second and first order, respectively, of perturbation theory. The computational scheme is essentially an eigenvalue problem of a Hermitian secular matrix defined with respect to the space of singly and doubly excited configurations. The configuration space is smaller (more compact) than that of comparable configuration interaction (CI) expansions and the method leads to size-consistent results. The performance of the ADC(2) method is tested in exemplary applications to Ne, Ar and CO, where detailed comparison can be made with experiment and previous theoretical results. While the accuracy of the absolute excitation energies is only moderate, a very satisfactory description is obtained for the relative energies and, in particular, for the spectral intensities. Aspects related to the Thomas-Reiche-Kuhn sum rule and the equivalence of the dipole-length and dipole-velocity forms of the transition moments are discussed. Due to the relatively small computational expense and the possibility of a direct ADC(2) formulation this method should prove particularly useful in applications to large molecules.

Multidimensional spectroscopy of photoreactivity

“…For the quantum-chemical calculations, only the ground-state geometry optimizations were performed on the B3LYP/cc-pVDZ level (38). Calibration calculations were performed using the highly accurate SCS-ADC(2)/cc-pVDZ approach as implemented in TURBOMOLE (39,40). On the basis of these results we selected the CAM-B3LYP (41) functional for the computation of the PESs using Gaussian 09 (42); this was necessary because solvent effects had to be taken into account, which is not possible for SCS-ADC(2).…”

The low-lying excited states of neutral polyacenes and their radical cations: a quantum chemical study employing the algebraic diagrammatic construction scheme of second order

“…Algebraic expressions of the ADC scheme for excited states have first been derived for closed-shell molecules employing diagrammatic perturbation theory of the polarization propagator using the typical Møller-Plesset partition of the Hamilton operator [33][34][35]54]. From that point of view, the choice of the otherwise unusual name becomes obvious.…”

“…(4)) are typical perturbation theoretical expressions, which have been derived in detail for ADC (2) and ADC(3) in Refs. [34][35][36]. Since the ADC(n) excitation energies are computed with respect to the corresponding MPn ground state, ADC(2), for instance, should only be applied to molecular systems whose ground state is well described by a single determinant such that MP2 is a reasonable approximation.…”

“…However, here one certainly faces all problems known from closed-shell systems [5]. An elegant, however, until today mostly overseen method for the calculation of excited states is the algebraic diagrammatic construction (ADC) scheme of the polarization propagator [33][34][35][36][37], originally derived in the realm of Green's function theory [38,39]. The recent development of efficient computer codes for ADC is a prerequisite for its routine application to molecular systems of chemical and biophysical interest [40][41][42][43].…”

Energetics and dynamics of a light-driven sodium-pumping rhodopsin

“…Recently, the structure of the first light-activated Na + pump, Krokinobacter eikastus rhodopsin 2 (KR2), was resolved at atomic resolution [Kato HE, et al (2015) Nature 521: [48][49][50][51][52][53]. To elucidate its molecular mechanism for Na + pumping, we perform here extensive classical and quantum molecular dynamics (MD) simulations of transient photocycle states.…”