The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

Entangled cadmium atoms - from the method of production to the test of Bell inequalities

We present recent progress in the implementation of experimental realization of a loophole-free test of Bell inequalities for entangled 111Cd atoms. The experimental approach is a modified version of the proposal of FRY and co-workers (Phys. Rev. A 52(6), 1995, p. 4381) for the realization of Bohm’s 1/2-spin particle version of the Einstein–Podolsky–Rosen (E-P-R) experiment and is based on the production of entangled atoms by photodissociation of the 111Cd2 isotopologue in a supersonic expansion beam using the spectroscopically selective stimulated Raman process

A program system for self-consistent embedded potentials for ionic crystals

Embedded-cluster models of crystalline solids are important to allow accurate wave function methods to be applicable to solids. The ab initio model potential method for embedding ionic solids has historically been shown to be a viable tool. While useful, the method has been limited by the need to generate such potentials for each crystal structure and the lack of a freely available program for generating ab initio model potentials. Herein, this is remedied by showcasing a new, AFL licensed, program, SCEPIC, which can be used in combination with Molcas or OpenMolcas codes to derive ab initio model potentials for ionic crystals. The applicability of ab initio model potentials derived via SCEPIC is evaluated for three simple ionic solids: MgO, CaO and CaF2. The following questions are addressed: (i) the capability of the method to reproduce the density matrix from periodic density functional theory calculations, (ii) the feasibility of performing geometry optimisations, (iii) the possibility to model band gaps of insulators and (iv) the ligand-field splitting of Ni-doped MgO. Going beyond the classical restriction of parametrising ab initio model potentials only at the Hartree–Fock level-of-theory, this work additionally address the sensitivity of results to the underlying Hamiltonian used to derive the potentials. The results demonstrate that good agreement with periodic density functional theory calculations can be achieved, geometry optimisations are feasible and accurate band gaps and ligand-field splittings can be computed

Absorption spectrum of Ca atoms attached to 4He nanodroplets

Within density functional theory, we have obtained the structure of 4 He droplets doped with neutral calcium atoms. These results have been used, in conjunction with newly determined ab initio 1 and 1 Ca-He pair potentials, to address the 4s4p 1 P1←4s2 1 S0 transition of the attached Ca atom, finding a fairly good agreement with absorption experimental data. We have studied the drop structure as a function of the position of the Ca atom with respect to the center of mass of the helium moiety. The interplay between the density oscillations arising from the helium intrinsic structure and the density oscillations produced by the impurity in its neighborhood plays a role in the determination of the equilibrium state, and hence in the solvation properties of alkaline earth atoms. In a case of study, the thermal motion of the impurity within the drop surface region has been analyzed in a semiquantitative way. We have found that, although the atomic shift shows a sizable dependence on the impurity location, the thermal effect is statistically small, contributing by about 10% to the line broadening. The structure of vortices attached to the calcium atom has been also addressed, and its effect on the calcium absorption spectrum discussed. At variance with previous theoretical predictions, we conclude that spectroscopic experiments on Ca atoms attached to 4 He drops will be likely unable to detect the presence of quantized vortices in helium nanodrops

Genetic algorithm for obtaining potential energy curve of diatomic molecules based on dispersed fluorescence spectra

Abstract The method for reconstruction of an adiabatic potential energy curve from experimental dispersed fluorescence spectra has been developed. The novelty of the method relies on a unique approach of simultaneous use of $$bound \rightarrow bound$$ b o u n d → b o u n d and $$bound \rightarrow free$$ b o u n d → f r e e parts of the spectrum. The method is based on the Genetic Algorithm (GA) procedure and determines potential energy curve integrally, below and above the dissociation energy limit. The method was tested on the artificially generated reference spectrum as well as experimental spectrum of $$G0_u^+(\upsilon ^{\prime }=39) \rightarrow X0_g^+$$ G 0 u + ( υ ′ = 39 ) → X 0 g + transition in Hg $$_2$$ 2 . The tests show very good accuracy of simulation based on GA results with artificially generated reference spectrum as well as with the experimental one