Modern quantum chemistry with [Open]Molcas

Artículo escrito por un elevado número de autores, sólo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereThe following article appeared in The Journal of Chemical Physics 152.21 (2020): 214117 and may be found at https://doi.org/10.1063/5.0004835MOLCAS/OpenMolcas is an ab initio electronic structure program providing a large set of computational methods from Hartree–Fock and density functional theory to various implementations of multiconfigurational theory. This article provides a comprehensive overview of the main features of the code, specifically reviewing the use of the code in previously reported chemical applications as well as more recent applications including the calculation of magnetic properties from optimized density matrix renormalization group wave functionsF.A. acknowledges financial support from the EU-H2020 research and innovation programme under Grant Agreement No. 654360 within the framework of the NFFA-Europe Transnational Access Activity. Part of this work was performed, thanks to computer resources provided by CINECA, under Project No. HPC-EUROPA3 (Grant No. INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action of the H2020 Programme. D.-C.S. and J.A. acknowledge support from the U.S. Department of Energy, Office of Basic Energy Sciences, Heavy Element Chemistry program, under Grant No. DE-SC0001136. S.B. acknowledges support from the Swiss National Science Foundation (Grant No. P2SKP2_184034). A.B. is grateful for support from ETH Zurich (ETH Fellowship No. FEL-49 18-1). M.R. acknowledges support from the Swiss National Science Foundation (Project No. 200021_182400). L.D.V., L.P.-G., and M.Ol. acknowledge a MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca) grant “Dipartimento di Eccellenza 2018-2022.” M.Ol. acknowledges NSF Grant No. CHE-CLP-1710191. M.D. and M.L. acknowledges support from the Olle Engkvist Foundation. E.D.L. and V.V. acknowledge computational resources provided by SNIC through LUNARC and NSC. T.B.P. acknowledges support from the Research Council of Norway through its Centres of Excellence scheme, Project No. 262695, and through Research Grant No. 240698. K.P. acknowledges financial support from KU Leuven through Grant No. C14/15/052. L.S. acknowledges financial support from Ministerio de Economía y Competitividad, Spain (Dirección General de Investigación y Gestión del Plan Nacional de I+D+i, Grant No. MAT2017-83553- P). J.S.-M. acknowledges support from the EU-H2020 Marie Curie Actions (AttoDNA, FP8-MSCA-IF, Grant No. 747662). I.S. gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant No. 678169 PhotoMutant). L.U. and X.G. gratefully acknowledge scientific Grant Nos. R-143-000-A80- 114 and R-143-000-A65-133 from the National University of Singapore. Computational resources of the NSCC (ASPIRE-1, Grant No. 11001278) were used for this study

Carbon K-edge x-ray emission spectroscopy of gas phase ethylenic molecules

We report on the C K-edge x-ray absorption spectra and the resonant (RXES) and non-resonant (NXES) x-ray emission spectra of ethylene, allene and butadiene in the gas phase. The RXES and NXES show clear differences for the different molecules. Overall both types of spectra are more structured for ethylene and allene, than for butadiene. Using density functional theory–restricted open shell configuration interaction single calculations, we simulate the spectra with remarkable agreement with the experiment. We identify the spectral features as being due to transitions involving localised 1s orbitals. For allene, there are distinct spectral bands that reflect transitions predominantly from either the central or terminal carbon atoms. These results are discussed in the context of ultrafast x-ray studies aimed at detecting the passage through conical intersections in polyatomic molecules

X-Ray Spectroscopy — The Driving Force to Understand and Develop Catalysis

Catalysis is involved in about 90% of manmade chemicals. The development of novel or improved catalysts requires fundamental understanding of the commanding steps of a catalytic reaction. In simple terms, a catalytic transformation depends on the coupling between catalyst electronic structure and reagents’ molecular orbitals. Herein, we report a spectroscopic technique capable of determining the electronic structure of metal containing catalysts under working conditions. The technique is called photon-in photon-out X-ray spectroscopy and can be employed to characterize materials, unveil substrate adsorption parameters, and follow changes in electronic structure during catalytic reactions

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

Photo initiated molecular processes elucidated by quantum chemistry and theoretical spectroscopy

Processes initiated by the interaction between light and matter are a fundamental step in various chemical, physical and biological phenomena. The present work investigates the photoinduced processes in artificial molecular machines and small molecules with the help of quantum chemical calculations. The research was performed in close collaboration with experimentalists, allowing an in-depth look at the underlying mechanisms of these ultrafast processes. The first part addresses the relaxation pathways after photoexcitation of the photoswitch hemithioindigo (HTI) and the artificial molecular motors, motor-1 and motor-2. The pho- tochromic compound HTI is a novel photoswitch capable of performing efficient isomerization upon irradiation with non-damaging visible light. Based on time-resolved absorption and emis- sion experiments and supported by high level quantum chemical calculations, a comprehensive reaction model for its photoisomerization, including the effects of different solvents as well as substitutions, is established. The structure of both molecular motors, motor-1 and motor-2, is based on the HTI moiety. By clever design, this switch was turned into a molecular motor, capable of unidirectional rotation. These motors are among the first light-powered molecular motors that operate under ambient and non-damaging conditions. The underlying processes for their multistep rotation was elucidated through multiscale broadband transient absorption mea- surements and quantum chemical investigations of their excited state potential energy surfaces. From these findings, pathways to improve the rotational speeds and efficiency of light-driven molecular motors in general could be developed. The second part of this work addresses the theoretical simulation of the ultrafast spec- troscopy technique known as attosecond transient absorption spectroscopy (ATAS). Attosecond pulses in the extreme ultraviolet (XUV) or X-ray region provide a powerful tool for investigating ultrafast nuclear and even electron dynamics in atoms, molecules and solids. Due to their high photon energy, they are able to create electron wave packets extremely well localized in time. This makes them an excellent choice for triggering photochemical reaction in a pump-probe scenario. Further, their broad bandwidth provides element, charge and electronic state sensitive insights by probing the inner-valence and core-level states of the excited molecules. To aid the interpretation of the experimental data and provide further insights into these complex inter- actions between light and matter, a comprehensive framework simulating XUV/X-ray transient absorption spectra is presented. Using ab initio non-adiabatic molecular dynamics (NAMD), the ultrafast processes of excited molecules after laser excitation is simulated, enabling the res- olution of both the changes in the electronic structure and the nuclear motion over time. Based on this information, the time-dependent XUV/X-ray transient absorption spectra are calculated by applying high-level multi-reference methods, namely restricted active space self-consistend field (RASSCF) and restricted active space perturbation theory (RASPT2). This framework is utilized in the two studies on the molecules vinyl bromide and trifluoroiodomethane. For both molecules the ultrafast coupled nuclear-electron dynamics after strong-field ionization could be explained in great detail

Theoretical X-ray Spectroscopy of Iron Complexes

This thesis discusses both theoretical developments for the calculation of X-ray spectra and applications of quantum-chemical methods to the calculation and interpretation of experimental X-ray spectra. The applications focus on the use of high-resolution experiments, which provide more detail in the spectra compared to conventional X-ray spectroscopy, on iron complexes. In particular, ferrocene derivatives and iron carbonyl complexes are considered