Beyond the random-phase approximation: A new approximation scheme for the polarization propagator

A hole in a 4d orbital of atomic xenon relaxes through Auger decay after a lifetime of 3 fs. Adding electronegative fluorine ligands to form xenon fluoride molecules, results in withdrawal of valenceelectron density from Xe. Thus, within the one-center picture of Auger decay, a lowered Xe 4d Auger width would be expected, in contradiction, however, with experiment. Employing extensive ab initio calculations within the framework of many-body Green's functions, we determine all available decay channels in XeFn and characterize these channels by means of a two-hole population analysis. We derive a relation between two-hole population numbers and partial Auger widths. On this basis, interatomic electronic decay processes are demonstrated to be so strong in the xenon fluorides that they overcompensate the reduction in intra-atomic Auger width and lead to the experimentally observed trend. The nature of the relevant processes is discussed. These processes presumably underlie Auger decay in a variety of systems.

Section: Computational Methods and Basic Relationsmentioning

confidence: 99%

Impact of interatomic electronic decay processes on Xe 4d hole decay in the xenon fluorides

Buth

Santra

Cederbaum

2003

“…Faster CC2 methods, such as the scaled-opposite-spin CC2 method, 51 which can be made to scale as N 4 with number of basis functions N, can be combined with the RVS approach to further increase efficiency and to treat even larger systems. The RVS approach is not limited to CC2 calculations but can also be used at more accurate correlation levels, in the second-order algebraic diagrammatic construction approximation (ADC(2)), 52 and also in TDDFT calculations as long as the uncertainty in the electron correlation treatment is larger than the RVS truncation error.…”

Section: A Embedded Systemsmentioning

confidence: 99%

Reduction of the virtual space for coupled-cluster excitation energies of large molecules and embedded systems

Send¹,

Kaila²,

Sundholm³

2011

We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50 eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1 eV. By using a RVS energy threshold of 50 eV, the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2/TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics/molecular mechanics separation schemes.

“…ADC [28][29][30] is based on a specific resummation of the perturbation series for the considered quantity and allows derivation of a set of systematic approximation schemes (ADC(n) schemes) which are complete through order n of perturbation theory (PT) and in addition contain infinite partial summations of the diagrammatic perturbation series. The starting point of the ADC approach is the observation that the exact (N − 2)-particle part Π II (ω) can be written in the general algebraic form…”

Section: The Methodsmentioning

confidence: 99%

Ab initio calculation of interatomic decay rates of excited doubly ionized states in clusters

Kolorenč

Averbukh

Gokhberg

et al. 2008

Recently, a computational technique for ab initio calculation of the inter-atomic and intermolecular non-radiative decay processes has been developed [1]. It combines the Fano formalism with the Green's function method known as the algebraic diagrammatic construction. The problem of normalization of continuum wave functions stemming from the use of the Gaussian basis sets is solved by using the Stieltjes imaging technique. In the present paper, the methodology is extended in order to describe the inter-atomic decay of excited doubly ionized states of clusters. The new computational scheme is applied to compute the inter-atomic decay rates of doubly ionized states formed by Auger relaxation of core vacancies in NeAr and MgNe van der Waals clusters.