Calculation Of Transition Properties Research Articles

Efficient and Parallel Implementation of Real and Complex Response Functions Employing the Second-Order Algebraic-Diagrammatic Construction Scheme for the Polarization Propagator.

We present the implementation of an efficient matrix-folded formalism for the evaluation of complex response functions and the calculation of transition properties at the level of the second-order algebraic-diagrammatic construction (ADC(2)) scheme. The underlying algorithms, in combination with the adopted hybrid MPI/OpenMP parallelization strategy, enabled calculations of the UV/vis spectra of a guanine oligomer series ranging up to 1032 contracted basis functions, thereby utilizing vast computational resources from up to 32,768 CPU cores. Further analysis of the convergence behavior of the involved iterative subspace algorithms revealed the superiority of a frequency-separated treatment of response equations even for a large spectral window, including 101 frequencies. We demonstrate the applicability to general quantum mechanical operators by the first reported electronic circular dichroism spectrum calculated with a complex polarization propagator approach at the ADC(2) level of theory.

Relativistic coupled-cluster calculations of transition properties in highly charged inert-gas ions

We have carried out an extensive investigation of various spectroscopic properties of highly charged inert-gas ions using a relativistic coupled-cluster method through a one-electron detachment procedure. In particular, we have calculated the atomic states $2{s}^{2}2{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{3/2}$, $2{s}^{2}2{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}$, and $2s2{p}^{6}\phantom{\rule{4pt}{0ex}}^{2}S_{1/2}$ in F-like inert-gas ions; $3{s}^{2}3{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{3/2}$, $3{s}^{2}3{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}$, and $3s3{p}^{6}\phantom{\rule{4pt}{0ex}}^{2}S_{1/2}$ states in Cl-like Kr, Xe, and Rn; and $4{s}^{2}4{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{3/2}$, $4{s}^{2}4{p}^{5}\phantom{\rule{4pt}{0ex}}^{2}P_{1/2}$, and $4s4{p}^{6}\phantom{\rule{4pt}{0ex}}^{2}S_{1/2}$ states in Br-like Xe and Rn. Starting from a single-reference Dirac-Hartree-Fock wave function, we construct our exact atomic states by including the dynamic correlation effects in an all-order perturbative fashion. Employing this method, we estimate the ionization potential energies of three low-lying orbitals present in their respective closed-shell configurations. Since the considered highly charged inert-gas ions exhibit huge relativistic effects, we have taken into account the corrections due to Breit interaction as well as from the dominant quantum electrodynamic correction such as vacuum polarization and self-energy effects in these systems. Using our calculated relativistic atomic wave functions and energies, we accurately determine various transition properties such as wavelengths, line strengths, oscillator strengths, transition probabilities, and lifetimes of the excited states.

On the difference between the transition properties calculated with linear response- and equation of motion-CCSD approaches

In this work, we quantitatively investigate the difference between the linear response (LR) and the equation of motion (EOM) coupled cluster (CC) approaches in the calculation of transition properties, namely, dipole and oscillator strengths, for the most widely used truncated CC wave function, which includes single and double excitation operators. We compare systems of increasing size, where the size-extensivity may be important. Our results suggest that, for small molecules, the difference is small even with large basis sets. The difference increases with the size of the system, but it is numerically small until hundreds of electron pairs are correlated. Although these calculations may be possible in a few years, at present the EOM approach is more advantageous, albeit more approximate, because it is computationally less demanding.

Automated calculation of anharmonic vibrational contributions to first hyperpolarizabilities: Quadratic response functions from vibrational configuration interaction wave functions

Quadratic response functions are derived and implemented for a vibrational configuration interaction state. Combined electronic and vibrational quadratic response functions are derived using Born-Oppenheimer vibronic product wave functions. Computational tractable expressions are derived for determining the total quadratic response contribution as a sum of contributions involving both electronic and vibrational linear and quadratic response functions. In the general frequency-dependent case this includes a new and more troublesome type of electronic linear response function. Pilot calculations for the FH, H(2)O, CH(2)O, and pyrrole molecules demonstrate the importance of vibrational contributions for accurate comparison to experiment and that the vibrational contributions in some cases can be very large. The calculation of transition properties between vibrational states is combined with sum-over-states expressions for analysis purposes. On the basis of this some simple analysis methods are suggested. Also, a preliminary study of the effect of finite lifetimes on quadratic response functions is presented.

A program for the complete expansion of jj-coupled symmetry functions into Slater determinants

Different applications of atomic structure theory favour different representations of the many-electron wave function. For an estimate of energy levels it is appropriate to start from symmetry adapted functions which keep the size of the Hamiltonian matrix to be diagonalized small. In the calculation of transition properties, on the other hand, the electron rearrangement during an atomic excitation or decay process can be effectively treated, if the wave functions are represented as linear combination of determinants. The relaxation of the electron density is naturally obtained in self-consistent-field calculations and is expressed in terms of the one-electron orbital functions, which are not quite orthogonal in the initial and final states of a transition. We provide a module to expand the symmetry adapted configuration and/or atomic states in the framework of the Oxford atomic structure program GRASP [F. A. Parpia and I. P. Grant, 1990] into a basis of Slater determinants which will be appropriate for forthcoming applications of the atomic multiconfiguration Dirac-Fock model.