| 1. |
- Aquilante, Francesco, et al.
(författare)
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Modern quantum chemistry with [Open]Molcas
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:21
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Tidskriftsartikel (refereegranskat)abstract
- MOLCAS/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 functions.
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| 2. |
- Aquilante, Francesco, et al.
(författare)
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Molcas 8 : New capabilities for multiconfigurational quantum chemical calculations across the periodic table
- 2016
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Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 37:5, s. 506-541
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Tidskriftsartikel (refereegranskat)abstract
- In this report, we summarize and describe the recent unique updates and additions to the Molcas quantum chemistry program suite as contained in release version 8. These updates include natural and spin orbitals for studies of magnetic properties, local and linear scaling methods for the Douglas-Kroll-Hess transformation, the generalized active space concept in MCSCF methods, a combination of multiconfigurational wave functions with density functional theory in the MC-PDFT method, additional methods for computation of magnetic properties, methods for diabatization, analytical gradients of state average complete active space SCF in association with density fitting, methods for constrained fragment optimization, large-scale parallel multireference configuration interaction including analytic gradients via the interface to the Columbus package, and approximations of the CASPT2 method to be used for computations of large systems. In addition, the report includes the description of a computational machinery for nonlinear optical spectroscopy through an interface to the QM/MM package Cobramm. Further, a module to run molecular dynamics simulations is added, two surface hopping algorithms are included to enable nonadiabatic calculations, and the DQ method for diabatization is added. Finally, we report on the subject of improvements with respects to alternative file options and parallelization.
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| 3. |
- Delcey, Mickael G., et al.
(författare)
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Exact semi-classical light-matter interaction operator applied to two-photon processes with strong relativistic effects
- 2020
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 153:2
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Tidskriftsartikel (refereegranskat)abstract
- X-ray processes involve interactions with high-energy photons. For these short wavelengths, the perturbing field cannot be treated as constant, and there is a need to go beyond the electric-dipole approximation. The exact semi-classical light-matter interaction operator offers several advantages compared to the multipole expansion such as improved stability and ease of implementation. Here, the exact operator is used to model x-ray scattering in metal K pre-edges. This is a relativistic two-photon process where absorption is dominated by electric-dipole forbidden transitions. With the restricted active space state-interaction approach, spectra can be calculated even for the multiconfigurational wavefunctions including second-order perturbation. However, as the operator itself depends on the transition energy, the cost for evaluating integrals for hundreds of thousands unique transitions becomes a bottleneck. Here, this is solved by calculating the integrals in a molecular-orbital basis that only runs over the active space, combined with a grouping scheme where the operator is the same for close-lying transitions. This speeds up the calculations of single-photon processes and is critical for the modeling of two-photon scattering processes. The new scheme is used to model Kα resonant inelastic x-ray scattering of iron-porphyrin complexes with relevance to studies of heme enzymes, for which the total computational time is reduced by several orders of magnitude with an effect on transition intensities of 0.1% or less.
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| 4. |
- Farahani, Pooria, 1985-, et al.
(författare)
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A combined theoretical and experimental study onthe mechanism of spiro-adamantyl-1,2-dioxetanone decomposition
- 2017
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 7, s. 17462-17472
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Tidskriftsartikel (refereegranskat)abstract
- 1,2-Dioxetanones have been considered as model compounds for bioluminescence processes. Theunimolecular decomposition of these prototypes leads mainly to the formation of triplet excited stateswhereas in the catalysed decomposition of these peroxides singlet states are formed preferentially.Notwithstanding, these cyclic peroxides are important models to understand the general principles ofchemiexcitation as they can be synthesised, purified and characterised. We report here results ofexperimental and theoretical approaches to investigating the decomposition mechanism of spiroadamantyl-1,2-dioxetanone. The activation parameters in the unimolecular decomposition of thisderivative have been determined by isothermal kinetic measurements (30–70 C) and thechemiluminescence activation energy calculated from the correlation of emission intensities. Theactivation energy for peroxide decomposition proved to be considerably lower than thechemiluminescence activation energy indicating the existence of different reaction pathways for groundand excited state formation. These experimental results are compared with the calculations at thecomplete active space second-order perturbation theory (CASPT2), which reveal a two-step biradicalmechanism starting by weak peroxide bond breakage followed by carbon–carbon elongation. Thetheoretical findings also indicate different transition state energies on the excited and ground statesurfaces during the C–C bond cleavage in agreement with the experimental activation parameters.
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| 5. |
- Farahani, Pooria, 1985-, et al.
(författare)
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Advances in computationalphotochemistry and chemiluminescenceof biological and nanotechnologicalmolecules
- 2017. - 44
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Ingår i: Photochemistry. - Cambridge, UK : Royal Society of Chemistry. - 1465-1947. ; , s. 16-60, s. 16-60
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Bokkapitel (refereegranskat)abstract
- Recent advances (2014–2015) in computational photochemistry and chemiluminescencederive from the development of theory and from the application of state-of-the-art andnew methodology to challenging electronic-structure problems. Method developmentshave mainly focused, first, on the improvement of approximate and cheap methods toprovide a better description of non-adiabatic processes, second, on the modification ofaccurate methods in order to decrease the computation time and, finally, on dynamicsapproaches able to provide information that can be directly compared with experimentaldata, such as yields and lifetimes. Applications of the ab initio quantum-chemistry methodshave given rise to relevant findings in distinct fields of the excited-state chemistry.We brieflysummarise, in this chapter, the achievements on photochemical mechanisms andchemically-induced excited-state phenomena of interest in biology and nanotechnology.
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| 6. |
- Galván, Ignacio Fdez., et al.
(författare)
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OpenMolcas : From Source Code to Insight
- 2019
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 15:11, s. 5925-5964
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Tidskriftsartikel (refereegranskat)abstract
- In this Article we describe the OpenMolcas environment and invite the computational chemistry community to collaborate. The open-source project already includes a large number of new developments realized during the transition from the commercial MOLCAS product to the open-source platform. The paper initially describes the technical details of the new software development platform. This is followed by brief presentations of many new methods, implementations, and features of the OpenMolcas program suite. These developments include novel wave function methods such as stochastic complete active space self-consistent field, density matrix renormalization group (DMRG) methods, and hybrid multiconfigurational wave function and density functional theory models. Some of these implementations include an array of additional options and functionalities. The paper proceeds and describes developments related to explorations of potential energy surfaces. Here we present methods for the optimization of conical intersections, the simulation of adiabatic and nonadiabatic molecular dynamics, and interfaces to tools for semiclassical and quantum mechanical nuclear dynamics. Furthermore, the Article describes features unique to simulations of spectroscopic and magnetic phenomena such as the exact semiclassical description of the interaction between light and matter, various X-ray processes, magnetic circular dichroism, and properties. Finally, the paper describes a number of built-in and add-on features to support the OpenMolcas platform with postcalculation analysis and visualization, a multiscale simulation option using frozen-density embedding theory, and new electronic and muonic basis sets.
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| 7. |
- Manni, Giovanni Li, et al.
(författare)
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The OpenMolcas Web : A Community-Driven Approach to Advancing Computational Chemistry
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:20, s. 6933-6991
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Sankari, Anna, et al.
(författare)
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Non-radiative decay and fragmentation in water molecules after 1a1-14a1 excitation and core ionization studied by electron-energy-resolved electron–ion coincidence spectroscopy
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:7
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examine decay and fragmentation of core-excited and core-ionized water molecules combining quantum chemical calculations and electron-energy-resolved electron–ion coincidence spectroscopy. The experimental technique allows us to connect electronic decay from core-excited states, electronic transitions between ionic states, and dissociation of the molecular ion. To this end, we calculate the minimum energy dissociation path of the core-excited molecule and the potential energy surfaces of the molecular ion. Our measurements highlight the role of ultra-fast nuclear motion in the 1a1-14a1 core-excited molecule in the production of fragment ions. OH+ fragments dominate for spectator Auger decay. Complete atomization after sequential fragmentation is also evident through detection of slow H+ fragments. Additional measurements of the non-resonant Auger decay of the core-ionized molecule (1a1-1) to the lower-energy dication states show that the formation of the OH+ + H+ ion pair dominates, whereas sequential fragmentation OH+ + H+ → O + H+ + H+ is observed for transitions to higher dication states, supporting previous theoretical investigations.
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| 9. |
- Schalk, Oliver, et al.
(författare)
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Competition between ring-puckering and ring-opening excited state reactions exemplified on 5H-furan-2-one and derivatives
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:6
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of ring-puckering on the light-induced ring-opening dynamics of heterocyclic compounds was studied on the sample 5-membered ring molecules gamma-valerolactone and 5H-furan-2-one using time-resolved photoelectron spectroscopy and ab initio molecular dynamics simulations. In gamma-valerolactone, ring-puckering is not a viable relaxation channel and the only available reaction pathway is ring-opening, which occurs within one vibrational period along the C-O bond. In 5H-furan-2-one, the C = C double bond in the ring allows for ring-puckering which slows down the ring-opening process by about 150 fs while only marginally reducing its quantum yield. This demonstrates that ring-puckering is an ultrafast process, which is directly accessible upon excitation and which spreads the excited state wave packet quickly enough to influence even the outcome of an otherwise expectedly direct ring-opening reaction.
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| 10. |
- Ugandi, Mihkel, et al.
(författare)
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Uncontracted basis sets for ab initio calculations of muonic atoms and molecules
- 2018
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 118:21
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we investigated muonic atoms and molecules from a quantum chemist's viewpoint by incorporating muons in the CASSCF model. With the aim of predicting muonic X-ray energies, primitive muonic basis sets were developed for a selection of elements. The basis sets were then used in CASSCF calculations of various atoms and molecules to calculate muonic excited states. We described the influence of nuclear charge distribution in predicting muonic X-ray energies. Effects of the electronic wave function on the muonic X-ray energies were also examined. We have computationally demonstrated how the muon can act as a probe for the nuclear charge distribution or electronic wave function by considering lower or higher muonic excited states, respectively.
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