| 1. |
- Aquilante, Francesco, et al.
(författare)
-
Modern quantum chemistry with [Open]Molcas
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:21
-
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.
|
|
| 2. |
- Aquilante, Francesco, et al.
(författare)
-
Molcas 8 : New capabilities for multiconfigurational quantum chemical calculations across the periodic table
- 2016
-
Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 37:5, s. 506-541
-
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.
|
|
| 3. |
- Aquilante, Francesco, et al.
(författare)
-
Software news and update MOLCAS 7 : The Next Generation
- 2010
-
Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 31:1, s. 224-247
-
Forskningsöversikt (refereegranskat)abstract
- Some of the new unique features of the MOLCAS quantum chemistry package version 7 are presented in this report. In particular, the Cholesky decomposition method applied to some quantum chemical methods is described. This approach is used both in the context of a straight forward approximation of the two-electron integrals and in the generation of so-called auxiliary basis sets. The article describes how the method is implemented for most known wave functions models: self-consistent field, density functional theory, 2nd order perturbation theory, complete-active space self-consistent field multiconfigurational reference 2nd order perturbation theory, and coupled-cluster methods. The report further elaborates on the implementation of a restricted-active space self-consistent field reference function in conjunction with 2nd order perturbation theory. The average atomic natural orbital basis for relativistic calculations, covering the whole periodic table, are described and associated unique properties are demonstrated. Furthermore, the use of the arbitrary order Douglas-Kroll-Hess transformation for one-component relativistic calculations and its implementation are discussed. This section especially focuses on the implementation of the so-called picture-change-free atomic orbital property integrals. Moreover, the ElectroStatic Potential Fitted scheme, a version of a quantum mechanics/molecular mechanics hybrid method implemented in MOLCAS, is described and discussed. Finally, the report discusses the use of the MOLCAS package for advanced studies of photo chemical phenomena and the usefulness of the algorithms for constrained geometry optimization in MOLCAS in association with such studies.
|
|
| 4. |
|
|
| 5. |
- Chen, Shu-Feng, et al.
(författare)
-
Chemiluminescence of Coelenterazine and Fluorescence of Coelenteramide : A Systematic Theoretical Study
- 2012
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 8:8, s. 2796-2807
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the structural and spectroscopic properties of coelenteramide has been performed at the TD-CAM-B3LYP/6-31+G(d,p) level of theory, including various fluorescence and chemiluminescence states. The influence of geometric conformations, solvent polarity, protonation state, and the covalent character of the O-H bond of the hydroxyphenyl moiety were carefully studied. Striking differences in geometries and electronic structures among the states responsible for light emission were characterized. All fluorescence states can be described as a limited charge transfer process for a planar amide moiety. However, the chemiluminescence state is characterized by a much larger charge transfer that takes place over a longer distance. Moreover, the chemiluminescent coelenteramide structure exhibits an amide moiety that is no longer planar, in agreement with recent, more accurate ab initio results [Roca-Sanjuan et al J. Chem. Theory Comput. 2011, 7, 4060] Because the chemiluminescence state appears to be completely dark, a new mechanism is tentatively introduced for this process.
|
|
| 6. |
- Chen, Shu-Feng, et al.
(författare)
-
Systematic theoretical investigation on the light emitter of firefly
- 2011
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 7:3, s. 798-803
-
Tidskriftsartikel (refereegranskat)abstract
- This is a systematic theoretical investigation on all the possible light emitters of firefly using multireference method. Six chemical forms of oxyluciferin (OxyLH2) molecules/anions were studied by a multi-state complete active space second order perturbation (MS-CASPT2) method in vacuum and DMSO. The calculated results and subsequent analysis excluded enol-OxyLH2, keto-OxyLH2 and enolate-OxyLH- as possible light emitters. The remaining three candidates, phenolate-enol-OxyLH-, phenolate-keto-OxyLH- and OxyL2-, were further investigated in protein by a MS-CASPT2/molecular mechanics (MM) study to explain the natural bioluminescence of firefly. By comparison of the MS-CASPT2/MM calculated results of phenolate-enol-OxyLH-, phenolate-keto-OxyLH- and OxyL2- with the experimental observation and detailed analysis, we concluded that the direct decomposition excited-state product of firefly dioxetanone in vivo and the only light emitter of firefly in natural bioluminescence is the first singlet exited state (S1) of phenolate-keto-OxyLH-.
|
|
| 7. |
- Chen, Shufeng, et al.
(författare)
-
Hybrid QM/MM Simulations of the Obelin Bioluminescence and Fluorescence Reveal an Unexpected Light Emitter
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:11, s. 2896-2903
-
Tidskriftsartikel (refereegranskat)abstract
- Obelia longissima, a tiny hydrozoan living in temperate and cold seas, features the Obelin photoprotein, which emits blue light. The Obelin bioluminescence and the Ca2+-discharged Obelin fluorescence spectra show multimodal characteristics that are currently interpreted by the concomitant participation of several light emitters. Up to now, the coelenteramide luminophore is thought to exist in different protonation states, one of them engaged in an ion-pair with the nearby residue, His22. Using hybrid quantum mechanics/molecular mechanics (QM/MM) calculations, we demonstrate that such an ion-pair cannot exist as a stable light emitter. However, when His22 electric neutrality is maintained by means of another proton transfer, the phenolate state of coelenteramide exhibits emission properties in agreement with experiment. Finally, an alternative nonradiative decay pathway, involving the formation of a diradical excited state, is postulated for the first time.
|
|
| 8. |
|
|
| 9. |
- Gozem, Samer, et al.
(författare)
-
Shape of Multireference, Equation-of-Motion Coupled-Cluster, and Density Functional Theory Potential Energy Surfaces at a Conical Intersection
- 2014
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 10:8, s. 3074-3084
-
Tidskriftsartikel (refereegranskat)abstract
- We report and characterize ground-state and excited-state potential energy profiles using a variety of electronic structure methods along a loop lying on the branching plane associated with a conical intersection (Cl) of a reduced retinal model, the penta-2,4-dieniminium cation (PSB3). Whereas the performance of the equation-of-motion coupled-duster, density functional theory, and multireference methods had been tested along the excited- and ground-state paths of PSB3 in our earlier work, the ability of these methods to correctly describe the potential energy surface shape along a CI branching plane has not yet been investigated. This is the focus of the present contribution. We find, in agreement with earlier studies by others, that standard time-dependent DFT (TDDFT) does not yield the correct two-dimensional (i.e., conical) crossing along the branching plane but rather a one-dimensional (i.e., linear) crossing along the same plane. The same type of behavior is found for SS-CASPT2(IPEA=0), SS-CASPT2(IPEA=0.25), spin-projected SF-TDDFT, EOM-SF-CCSD, and, finally, for the reference MRCISD+Q method. In contrast, we found that MRCISD, CASSCF, MS-CASPT2(IPEA=0), MS-CASPT2(IPEA=0.25), XMCQDPT2, QD-NEVPT2, non-spin-projected SF-TDDFT, and SI-SA-REKS yield the expected conical crossing. To assess the effect of the different crossing topologies (i.e., linear or conical) on the PSB3 photoisomerization efficiency, we discuss the results of 100 semiclassical trajectories computed by CASSCF and SS-CASPT2(IPEA=0.25) for a PSB3 derivative. We show that for the same initial conditions, the two methods yield similar dynamics leading to isomerization quantum yields that differ by only a few percent.
|
|
| 10. |
- Manni, Giovanni Li, et al.
(författare)
-
The OpenMolcas Web : A Community-Driven Approach to Advancing Computational Chemistry
- 2023
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:20, s. 6933-6991
-
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.
|
|
| 11. |
- Melaccio, Federico, et al.
(författare)
-
Unique QM/MM potential energy surface exploration using microiterations
- 2011
-
Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 111:13, s. 3339-3346
-
Tidskriftsartikel (refereegranskat)abstract
- The determination and the characterization of important points of a potential energy surface can be carried out routinely using any molecular modelling software based on either a quantum mechanical (QM) or a classical (molecular mechanics, MM) description of the particle interactions. However the coupling of the QM and MM descriptions (QM/MM) gives rise to severe efficiency limitations during a geometry optimization of the whole system, especially when both subsystems are coupled electrostatically. The present work introduces two simple improvements, mainly developed in the framework of the ElectroStatic Potential Fitted (ESPF) method to ensure the uniqueness of the QM/MM potential energy surface. The first one aims to improve the approximate Hessian matrix used in the QM optimization step. The second one tries to recouple electrostatically the QM and MM subsystems when microiterations are used. These methods are tested on a very simple system (a QM water molecule in a MM water box) before to be applied to the investigation of the light absorption in the rhodopsin protein at the multireference second-order perturbation level of theory (CASPT2). This work is dedicated to the memory of Prof. B. O. Roos. He was a great support for the implementation of the QM/MM method in the Molcas package.
|
|
| 12. |
- Navizet, Isabelle, et al.
(författare)
-
Are the Bio- and Chemiluminescence States of the Firefly Oxyluciferin the Same as the Fluorescence State?
- 2013
-
Ingår i: Photochemistry and Photobiology. - : Wiley. - 0031-8655 .- 1751-1097. ; 89:2, s. 319-325
-
Tidskriftsartikel (refereegranskat)abstract
- A usual strategy in both experimental and theoretical studies on bio- and chemiluminescence is to analyze the fluorescent properties of the bio- and chemiluminescence reaction product. Recent findings in a coelenteramide and Cypridina oxyluciferin model arise a concern on the validity of this procedure, showing that the light emitters in each of these luminescent processes might differ. Here, the thermal decomposition path of the firefly dioxetanone and the light emission states of the Firefly oxyluciferin responsible for the bio-, chemiluminescence, and fluorescence of the molecule are characterized using ab initio quantum chemistry and hybrid quantum chemistry/molecular mechanics methods to determine if the scenario found in the coelenteramide and Cypridina oxyluciferin study does also apply to the Firefly bioluminescent systems. The results point out to a unique emission state in the bio-, chemiluminescence, and fluorescence phenomena of the Firefly oxyluciferin and, therefore, using fluorescence properties of this system is reasonable.
|
|
| 13. |
|
|
| 14. |
- Navizet, Isabelle, et al.
(författare)
-
Color-Tuning Mechanism of Firefly Investigated by Multi-Configurational Perturbation Method
- 2010
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 132:2, s. 706-712
-
Tidskriftsartikel (refereegranskat)abstract
- This is the first report on a multiconfigurational reference second-order perturbation theory−molecular mechanics study of the color modulation of the observed bioluminescence of the oxyluciferin−luciferase complex of the Japanese genji-botaru firefly using structures according to recent X-ray data. Our theoretical results do not support the experimentally deduced conclusion that the color modulation of the emitted light primarily depends on the size of the compact luciferase protein cavity embedding the excited oxyluciferin molecule. Rather, we find, in agreement with recent experimental observations, that the wavelength of the emitted light depends on the polarity of the microenvironment at the phenol/phenolate terminal of the benzothiazole fragment in oxyluciferin.
|
|
| 15. |
|
|
| 16. |
- Navizet, Isabelle, et al.
(författare)
-
The Chemistry of Bioluminescence : An Analysis of Chemical Functionalities
- 2011
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 12:17, s. 3064-3076
-
Forskningsöversikt (refereegranskat)abstract
- Firefly luciferase is one of the most studied bioluminescent systems, both theoretically and experimentally. Herein we review the current understanding of the bioluminescent process from a chemical functionality perspective based on those investigations. Three key components are emphasized: the chemiluminophore, the electron-donating fragment, and how these are affected by the substrateenzyme interaction. The understanding is based on details of how the peroxide ?O?O? bond supports the production of electronically excited products and how the charge-transfer (CT) mechanism, with the aid of an electron-donating group, lowers the activation barrier to support a reaction occurs in living organisms. For the substrateenzyme complex it is demonstrated that the enzyme can affect the hydrogen-bonding around the CT-controlling group, resulting in a mechanism for color modulation. Finally, we analyse other luciferinluciferase systems and compare them to the key chemical functionalities of the fragments of the luciferinluciferase complex with respect to similarities and differences.
|
|
| 17. |
|
|
| 18. |
- Roca-Sanjuán, Daniel, et al.
(författare)
-
Chemiluminescence and Fluorescence States of a Small Model for Coelenteramide and Cypridina Oxyluciferin : A CASSCF/CASPT2 Study
- 2011
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 7:12, s. 4060-4069
-
Tidskriftsartikel (refereegranskat)abstract
- Fluorescence and chemiluminescence phenomena are often confused in experimental and theoretical studies on the luminescent properties of chemical systems. To establish the patterns that distinguish both processes, the fluorescent and chemiluminescent states of 2-acetamido-3-methylpyrazine, which is a small model of the coelenterazine/coelenteramide and Cypridina luciferin/oxyluciferin bioluminescent systems, were characterized by using the complete active space second-order perturbation (CASPT2) method. Differences in geometries and electronic structures among the states responsible for light emission were found. On the basis of the findings, some recommendations for experimental studies on chemiluminescence are suggested, and more appropriate theoretical approaches are proposed.
|
|
| 19. |
|
|
| 20. |
- Schapiro, Igor, et al.
(författare)
-
The Ultrafast Photoisomerizations of Rhodopsin and Bathorhodopsin Are Modulated by Bond Length Alternation and HOOP Driven Electronic Effects
- 2011
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:10, s. 3354-3364
-
Tidskriftsartikel (refereegranskat)abstract
- Rhodopsin (Rh) and bathorhodopsin (bathoRh) quantum-mechanics/molecular-mechanics models based on ab initio multiconfigurational wave functions are employed to look at the light induced π-bond breaking and reconstitution occurring during the RhfbathoRh and bathoRhfRh isomerizations. More specifically, semiclassical trajectory computations are used to compare the excited (S1) and ground (S0) state dynamics characterizing the opposite steps of the Rh/bathoRh photochromic cycle during the first 200 fs following photoexcitation. We show that the information contained in these data provide an unprecedented insight into the sub-picosecond π-bond reconstitution process which is at the basis of the reactivity of the protein embedded 11-cis and all-trans retinal chromophores.More specifically, the data point to the phase and amplitude of the skeletal bond length alternation stretchingmode as the key factor switching the chromophore to a bonding state. It is also confirmed/found that the phase and amplitude of the hydrogen-out-of-plane mode controls the stereochemical outcome of the forward and reverse photoisomerizations.
|
|
| 21. |
|
|
| 22. |
- Strambi, Angela, et al.
(författare)
-
Anabaena sensory rhodopsin is a light-driven unidirectional rotor
- 2010
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 107:50, s. 21322-21326
-
Tidskriftsartikel (refereegranskat)abstract
- The implementation of multiconfigurational quantum chemistry methods into a quantum-mechanics/molecular-mechanics protocol has allowed the construction of a realistic computer model for the sensory rhodopsin of the cyanobacterium Anabaena PCC 7120. The model, which reproduces the absorption spectra of both the all-trans and 13-cis forms of the protein and their associated K and L intermediates, is employed to investigate the light-driven steps of the photochromic cycle exhibited by the protein. It is found that the photoisomerizations of the all-trans and 13-cis retinal chromophores occur through unidirectional, counterclockwise 180 deg rotations of the =C14-C15= moiety with respect to the Lys210-linked end of the chromophore axis. Thus, the sequential interconversions of the all-trans and 13-cis forms during a single photochromic cycle yield a complete (360 deg) unidirectional rotation of the =C14-C15= moiety. This finding implies that Anabaena sensory rhodopsin is a biological realization of a light-driven molecular rotor.
|
|
| 23. |
- Vacher, Morgane, et al.
(författare)
-
Chemi- and Bioluminescence of Cyclic Peroxides
- 2018
-
Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 118:15, s. 6927-6974
-
Forskningsöversikt (refereegranskat)abstract
- Bioluminescence is a phenomenon that has fascinated mankind for centuries. Today the phenomenon and its sibling, chemiluminescence, have impacted society with a number of useful applications in fields like analytical chemistry and medicine, just to mention two. In this review, a molecular-orbital perspective is adopted to explain the chemistry behind chemiexcitation in both chemi- and bioluminescence. First, the uncatalyzed thermal dissociation of 1,2-dioxetane is presented and analyzed to explain, for example, the preference for triplet excited product states and increased yield with larger nonreactive substituents. The catalyzed fragmentation reaction and related details are then exemplified with substituted 1,2-dioxetanone species. In particular, the preference for singlet excited product states in that case is explained. The review also examines the diversity of specific solutions both in Nature and in artificial systems and the difficulties in identifying the emitting species and unraveling the color modulation process. The related subject of excited-state chemistry without light absorption is finally discussed. The content of this review should be an inspiration to human design of new molecular systems expressing unique light-emitting properties. An appendix describing the state-of-the-art experimental and theoretical methods used to study the phenomena serves as a complement.
|
|
| 24. |
- Yue, Ling, et al.
(författare)
-
Can the Closed-Shell DFT Methods Describe the Thermolysis of 1,2-Dioxetanone?
- 2012
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 8:11, s. 4359-4363
-
Tidskriftsartikel (refereegranskat)abstract
- The chemiluminescent decomposition of 1,2-dioxetanone has in the past been studied by state-of-the-art multireference quantum chemical calculations, and a stepwise biradical mechanism was established. Recently, this decomposition has been reinvestigated, and a concerted mechanism has been proposed based on calculations performed at the closed-shell density functional theory (DFT) level of theory. In order to solve this apparent mechanistic contradiction, the present paper presents restricted and unrestricted DFT results obtained using functionals including different amounts of Hartree–Fock (HF) exchange, repeating and complementing the above-mentioned DFT calculations. The calculated results clearly indicate that the closed-shell DFT methods cannot correctly describe the thermolysis of 1,2-dioxetanone. It is found that unrestricted Kohn–Sham reaction energies and barriers are always lower than the ones obtained using a restricted formalism. Hence, from energy principles, the biradical mechanism is found to be prevailing in the understanding of the 1,2-dioxetanone thermolysis.
|
|
