Abstractorbkit is a toolbox for post-processing electronic structure calculations based on a highly modular and portable Python architecture. The program allows computing a multitude of electronic properties of molecular systems on arbitrary spatial grids from the basis set representation of its electronic wavefunction, as well as several gridindependent properties. The required data can be extracted directly from the standard output of a large number of quantum chemical programs. orbkit can be used as a standalone program to determine standard quantities, for example, the electron density, molecular orbitals, and derivatives thereof. The cornerstone of orbkit is its modular structure. The existing basic functions can be arranged in an individual way and can be easily extended by user-written modules to determine any other desired quantities. orbkit offers multiple output formats that can be processed by common visualization tools (VMD, Molden, etc.). Additionally, orbkit possesses routines to order molecular orbitals computed at different nuclear configurations according to their electronic character and to interpolate the wavefunction between these configurations. The program is open-source under GNU-LGPLv3 license and freely available at http://sourceforge.net/projects/orbkit/. This article provides an overview of orbkit with particular focus on its capabilities and applicability, and includes several example calculations.Keywords: quantum chemical calculation, electronic structure, molecular visualization, electron density, grid representation of one-electron quantities, molecular orbital ordering * Institut für Chemie und Biochemie, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany † These authors contributed equally to this work. orbkit is an open-source toolbox for post-processing electronic structure calculations. Based on a highly modular and portable Python architecture, it comes both as a standalone program and a function library. The program allows computing electronic properties of molecular systems on arbitrary spatial grids from the output of standard quantum chemistry programs.2

No abstract

Correlated, multielectron dynamics of "open" electronic systems within the fixed-nuclei approximation are treated here within explicitly time-dependent configuration-interaction schemes. Specifically, we present simulations of laser-pulse driven excitations of selected electronic states of LiCN in the presence of energy and phase relaxation. The evolution of the system is studied using open-system density matrix theory, which embeds naturally in the time-dependent configuration-interaction singles (doubles) formalism. Different models for dissipation based on the Lindblad semigroup formalism are presented. These models give rise to lifetimes for energy relaxation ranging from a few hundreds of femtoseconds to several nanoseconds. Pure dephasing is treated using a Kossakowski-like Gaussian model, proceeding on similar time scales. The pulse lengths employed range from very short (tens of femtoseconds) to very long (several nanoseconds). To make long-time propagations tractable, the quasiresonant approximation is used. The results show that despite the loss of efficiency, selective dipole switching can still be achieved in the presence of dissipation when using appropriately designed laser pulses.

No abstract

Two different sets of approaches for the density-functional calculation of the spin-orbit contributions to zero-field splitting (ZFS) parameters of high-spin systems have been implemented within the same quantum chemistry code ReSpect and have been validated and compared for a series of model systems. The first approach includes spin-orbit coupling variationally in a two-component calculation, using either an all-electron Douglas-Kroll-Hess ansatz or two-component relativistic pseudopotentials. The ZFS parameters are computed directly from energy differences between different relativistic states. Additionally, an approximate second-order perturbation theory approach has been implemented, based on nonrelativistic or scalar relativistic wave functions. For a series of group 16 triplet diatomics and for the octet GdH3 molecules, two-component density functional calculations underestimate the zero-field splitting D systematically by a factor of 2. This may be rationalized readily by the incomplete description of states with absolute value MJ < J by a single-determinantal wave function built from two-component spinors. In the case of two 3d transition metal complexes and for GdH3, the results depend furthermore sensitively on exchange-correlation functional. Results of the alternative one-component approach agree strikingly with the two-component data for systems with small spin-orbit effects and start to deviate from them only for heavier systems with large spin-orbit effects. These results have fundamental implications for the achievable accuracy of one-component density-functional approaches used widely to compute ZFS parameters in the field of molecular magnetism. Possible refinements of both one-and two-component approaches are discussed.

The desorption of molecular hydrogen and deuterium induced by femtosecond-laser pulses is studied theoretically for the so-called DIMET (Desorption Induced by Multiple Electronic Transitions) process. These investigations are based on nonadiabatic classical Monte Carlo trajectory (CMCT) simulations on a ground and an excited state potential energy surface, including up to all six adsorbate degrees of freedom. The focus is on the hot-electron mediated energy transfer from the surface to the molecule and back, and the energy partitioning between the different degrees of freedom of the desorbing molecules. We first validate for a two-mode model comprising the desorption mode and the internal vibrational coordinate, the classical Monte Carlo trajectory method by comparing with Monte Carlo wavepacket (MCWP) calculations arising from a fully quantum mechanical open-system density matrix treatment. We then proceed by extending the CMCT calculations to include all six nuclear degrees of freedom of the desorbing molecule. This allows for a detailed comparison between theory and experiment concerning isotope effects, energy partitioning (translational, vibrational, and rotational energies and their distributions), and the dependence of these properties on the laser fluence. The most important findings are as follows. (i) CMCT agrees qualitative with the MCWP scheme. (ii) The basic experimental features such as the large isotope effect, the non-linear increase of yield with laser fluence, translationally hot products (in the order of several 1000 K) and non-equipartitioning of translational and internal energies (E(trans) > E(vib) > E(rot)) are well reproduced. (iii) Predictions concerning a strong angular dependence of translational energies at large observation angles are also made.

The aim of the present contribution is to provide a framework for analyzing and visualizing the correlated many-electron dynamics of molecular systems, where an explicitly time-dependent electronic wave packet is represented as a linear combination of N -electron wave functions. The central quantity of interest is the electronic flux density, which contains all information about the transient electronic density, the associated phase, and their temporal evolution. It is computed from the associated one-electron operator by reducing the multi-determinantal, many-electron wave packet using the Slater-Condon rules. Here, we introduce a general tool for post-processing multi-determinant configuration-interaction wave functions obtained at various levels of theory. It is tailored to extract directly the data from the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions. The procedure is implemented in the open-source Python program detCI@ORBKIT, which shares and builds upon the modular design of our recently published post-processing toolbox [J. Comput. Chem. 37 (2016) 1511]. The new procedure is applied to ultrafast charge migration processes in different molecular systems, demonstrating its broad applicability.Convergence of the N -electron dynamics with respect to the electronic structure theory level and basis set size is investigated. This provides an assessment of the robustness of qualitative and quantitative statements that can be made concerning dynamical features observed in charge migration simulations.

In this contribution, we extend our framework for analyzing and visualizing correlated many-electron dynamics to non-variational, highly scalable electronic structure method. Specifically, an explicitly time-dependent electronic wave packet is written as a linear combination of N-electron wave functions at the configuration interaction singles (CIS) level, which are obtained from a reference time-dependent density functional theory (TDDFT) calculation. The procedure is implemented in the open-source Python program detCI@ORBKIT, which extends the capabilities of our recently published post-processing toolbox (Hermann et al., J. Comput. Chem. 2016, 37, 1511). From the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions, the framework exploits the multideterminental structure of the hybrid TDDFT/CIS wave packet to compute fundamental one-electron quantities such as difference electronic densities, transient electronic flux densities, and transition dipole moments. The hybrid scheme is benchmarked against wave function data for the laser-driven state selective excitation in LiH. It is shown that all features of the electron dynamics are in good quantitative agreement with the higher-level method provided a judicious choice of functional is made. Broadband excitation of a medium-sized organic chromophore further demonstrates the scalability of the method. In addition, the time-dependent flux densities unravel the mechanistic details of the simulated charge migration process at a glance. © 2017 Wiley Periodicals, Inc.