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Couto, Rafael CarvalhoORCID iD iconorcid.org/0000-0003-4020-0923
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Publications (10 of 23) Show all publications
Chakraborty, P., Couto, R. C. & Holmgaard List, N. (2023). Deciphering Methylation Effects on S2(ππ*) Internal Conversion in the Simplest Linear α,β-Unsaturated Carbonyl. Journal of Physical Chemistry A, 127(25), 5360-5373
Open this publication in new window or tab >>Deciphering Methylation Effects on S2(ππ*) Internal Conversion in the Simplest Linear α,β-Unsaturated Carbonyl
2023 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 127, no 25, p. 5360-5373Article in journal (Refereed) Published
Abstract [en]

Chemical substituents can influence photodynamics by altering the location of critical points and the topography of the potential energy surfaces (electronic effect) and by selectively modifying the inertia of specific nuclear modes (inertial effects). Using nonadiabatic dynamics simulations, we investigate the impact of methylation on S2(ππ*) internal conversion in acrolein, the simplest linear α,β-unsaturated carbonyl. Consistent with time constants reported in a previous time-resolved photoelectron spectroscopy study, S2 → S1 deactivation occurs on an ultrafast time scale (∼50 fs). However, our simulations do not corroborate the sequential decay model used to fit the experiment. Instead, upon reaching the S1 state, the wavepacket bifurcates: a portion undergoes ballistic S1 → S0 deactivation (∼90 fs) mediated by fast bond-length alternation motion, while the remaining decays on the picosecond time scale. Our analysis reveals that methyl substitution, generally assumed to mainly exert inertial influence, is also manifested in important electronic effects due to its weak electron-donating ability. While methylation at the β C atom gives rise to effects principally of an inertial nature, such as retarding the twisting motion of the terminal −CHCH3 group and increasing its coupling with pyramidalization, methylation at the α or carbonyl C atom modifies the potential energy surfaces in a way that also contributes to altering the late S1-decay behavior. Specifically, our results suggest that the observed slowing of the picosecond component upon α-methylation is a consequence of a tighter surface and reduced amplitude along the central pyramidalization, effectively restricting the access to the S1/S0-intersection seam. Our work offers new insight into the S2(ππ*) internal conversion mechanisms in acrolein and its methylated derivatives and highlights site-selective methylation as a tuning knob to manipulate photochemical reactions.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
National Category
Atom and Molecular Physics and Optics Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-333915 (URN)10.1021/acs.jpca.3c02582 (DOI)001011694000001 ()37331016 (PubMedID)2-s2.0-85164211073 (Scopus ID)
Note

QC 20230816

Available from: 2023-08-16 Created: 2023-08-16 Last updated: 2023-09-05Bibliographically approved
Idebohn, V., Linguerri, R., Cornetta, L. M., Olsson, E., Wallner, M., Squibb, R. J., . . . Feifel, R. (2023). Symmetry breaking in core-valence double ionisation of allene. Communications Chemistry, 6(1), Article ID 137.
Open this publication in new window or tab >>Symmetry breaking in core-valence double ionisation of allene
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2023 (English)In: Communications Chemistry, E-ISSN 2399-3669, Vol. 6, no 1, article id 137Article in journal (Refereed) Published
Abstract [en]

Allene serves as a model to study multiple ionization of organic molecules. Here, the authors use synchrotron radiation-based multi-particle coincidence techniques and high-level ab initio calculations to propose a simple physical model to elucidate the symmetry breaking in core-valence double ionization of allene. Conventional electron spectroscopy is an established one-electron-at-the-time method for revealing the electronic structure and dynamics of either valence or inner shell ionized systems. By combining an electron-electron coincidence technique with the use of soft X-radiation we have measured a double ionisation spectrum of the allene molecule in which one electron is removed from a C1s core orbital and one from a valence orbital, well beyond Siegbahns Electron-Spectroscopy-for-Chemical-Analysis method. This core-valence double ionisation spectrum shows the effect of symmetry breaking in an extraordinary way, when the core electron is ejected from one of the two outer carbon atoms. To explain the spectrum we present a new theoretical approach combining the benefits of a full self-consistent field approach with those of perturbation methods and multi-configurational techniques, thus establishing a powerful tool to reveal molecular orbital symmetry breaking on such an organic molecule, going beyond Lowdins standard definition of electron correlation.

Place, publisher, year, edition, pages
Springer Nature, 2023
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-332206 (URN)10.1038/s42004-023-00934-1 (DOI)001021486700002 ()37400533 (PubMedID)2-s2.0-85163928721 (Scopus ID)
Note

QC 20230721

Available from: 2023-07-21 Created: 2023-07-21 Last updated: 2023-07-21Bibliographically approved
Manni, G. L., Galvan, I. F., Couto, R. C., Delcey, M. G. & Lindh, R. (2023). The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry. Journal of Chemical Theory and Computation, 19(20), 6933-6991
Open this publication in new window or tab >>The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry
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2023 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 19, no 20, p. 6933-6991Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-340989 (URN)10.1021/acs.jctc.3c00182 (DOI)001091999700001 ()37216210 (PubMedID)2-s2.0-85162813210 (Scopus ID)
Note

QC 20231218

Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2024-03-15Bibliographically approved
Lindblad, R., Kjellsson, L., De Santis, E., Zamudio-Bayer, V., von Issendorff, B., Sorensen, S. L., . . . Couto, R. C. (2022). Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 106(4), Article ID 042814.
Open this publication in new window or tab >>Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO
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2022 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 106, no 4, article id 042814Article in journal (Refereed) Published
Abstract [en]

Experimental near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the nitrosonium NO+ ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed-shell species, which for NEXAFS leads to the simplicity of a closed-shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the pi* resonance, and a shift of the sigma* resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO+ are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed-shell species NO+, N2, and N2H+.

Place, publisher, year, edition, pages
American Physical Society (APS), 2022
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-322871 (URN)10.1103/PhysRevA.106.042814 (DOI)000879523600001 ()2-s2.0-85141596315 (Scopus ID)
Note

QC 20230109

Available from: 2023-01-09 Created: 2023-01-09 Last updated: 2023-01-09Bibliographically approved
Carravetta, V., Couto, R. C. & Agren, H. (2022). X-ray absorption of molecular cations-a new challenge for electronic structure theory. Journal of Physics: Condensed Matter, 34(36), 363002, Article ID 363002.
Open this publication in new window or tab >>X-ray absorption of molecular cations-a new challenge for electronic structure theory
2022 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 34, no 36, p. 363002-, article id 363002Article, review/survey (Refereed) Published
Abstract [en]

In this paper we put forward some historical notes on the development of computational chemistry toward applications of x-ray spectroscopies. We highlight some of the important contributions by Enrico Clementi as method and program developer and as a supporter of this branch of computational research. We bring up a modern example based on the very recent experimental development of x-ray absorption of cationic molecules. As we show this spectroscopy poses new challenges for electronic structure theory and the electron correlation problem.

Place, publisher, year, edition, pages
IOP Publishing, 2022
Keywords
computational x-ray spectroscopy, NEXAFS, molecular cations
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-315921 (URN)10.1088/1361-648X/ac7d2a (DOI)000825736400001 ()35767974 (PubMedID)2-s2.0-85134426575 (Scopus ID)
Note

QC 20220728

Available from: 2022-07-28 Created: 2022-07-28 Last updated: 2022-07-28Bibliographically approved
Couto, R. C., Hua, W., Lindblad, R., Kjellsson, L., Sorensen, S. L., Kubin, M., . . . Carravetta, V. (2021). Breaking inversion symmetry by protonation: Experimental and theoretical NEXAFS study of the diazynium ion, N2H+. Physical Chemistry, Chemical Physics - PCCP, 23(32), 17166-17176
Open this publication in new window or tab >>Breaking inversion symmetry by protonation: Experimental and theoretical NEXAFS study of the diazynium ion, N2H+
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2021 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, no 32, p. 17166-17176Article in journal (Refereed) Published
Abstract [en]

As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion N2H+. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π∗ band, and a nitrogen 1s to H+ charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π∗ transitions are separated by 0.23 eV, only slightly exceeding the difference in the corresponding dark (symmetry forbidden) and bright (symmetry allowed) core excitations of neutral N2. By DFT and calculations and vibrational analysis, the complex π∗ excitation band of N2H+ is understood as due to the superposition of the significantly different vibrational progressions of excitations from terminal and central nitrogen atoms, both leading to bent final state geometries. We also show computationally that the electronic structure of the charge transfer excitation smoothly depends on the nitrogen-proton distance and that there is a clear extension of the spectra going from infinity to close nitrogen-proton distance where fine structures show some, although not fully detailed, similarities. An interesting feature of partial localization of the nitrogen core orbitals, with a strong, non-monotonous, variation with nitrogen-proton distance could be highlighted. Specific effects could be unraveled when comparing molecular cation NEXAFS spectra, as represented by recently recorded spectra of N2+ and CO+, and spectra of protonated molecules as represented here by the N2H+ ion. Both types containing rich physical effects not represented in NEXAFS of neutral molecules because of the positive charge, whereas protonation also breaks the symmetry. The effect of the protonation on dinitrogen can be separated in charge, which extends the high-energy part of the spectrum, and symmetry-breaking, which is most clearly seen in the low-energy π∗ transition.

Place, publisher, year, edition, pages
Royal Society of Chemistry (RSC), 2021
Keywords
Absorption spectroscopy, Calculations, Charge transfer, Electronic structure, Excited states, Ions, Molecules, Nitrogen, Ab initio calculations, Charge transfer bands, Charge-transfer excitations, Partial localization, Protonated molecules, Protonated species, Vibrational analysis, Vibrational progressions, Protonation
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-311201 (URN)10.1039/d1cp02002a (DOI)000680883900001 ()34346432 (PubMedID)2-s2.0-85113469793 (Scopus ID)
Note

QC 20220425

Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2022-06-25Bibliographically approved
Delcey, M. G., Couto, R. C., Kragh Sørensen, L., Galvan, I. F., Guo, M., Lindh, R. & Lundberg, M. (2020). Exact semi-classical light-matter interaction operator applied to two-photon processes with strong relativistic effects. Journal of Chemical Physics, 153(2), Article ID 024114.
Open this publication in new window or tab >>Exact semi-classical light-matter interaction operator applied to two-photon processes with strong relativistic effects
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2020 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 153, no 2, article id 024114Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2020
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-279212 (URN)10.1063/5.0007833 (DOI)000551896400006 ()32668952 (PubMedID)2-s2.0-85088158211 (Scopus ID)
Note

QC 20200903

Available from: 2020-09-03 Created: 2020-09-03 Last updated: 2024-03-18Bibliographically approved
Couto, R. C., Kjellsson, L., Ågren, H., Carravetta, V., Sorensen, S. L., Kubin, M., . . . Lindblad, R. (2020). The carbon and oxygen K-edge NEXAFS spectra of CO+. Physical Chemistry, Chemical Physics - PCCP, 22(28), 16215-16223
Open this publication in new window or tab >>The carbon and oxygen K-edge NEXAFS spectra of CO+
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2020 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 28, p. 16215-16223Article in journal (Refereed) Published
Abstract [en]

We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO(+)at the carbon and oxygen K-edges. The spectra show a wealth of features that appear very differently at the two K-edges. The analysis of these features can be divided into three parts; (i) repopulation transition to the open shell orbital - here the C(1s) or O(1s) to 5 sigma transition, where the normal core hole state is reached from a different initial state and different interaction than in X-ray photoelectron spectroscopy; (ii) spin coupled split valence bands corresponding to C(1s) or O(1s) to pi* transitions; (iii) remainder weak and long progressions towards the double ionization potentials containing a manifold of peaks. These parts, none of which has correspondence in NEXAFS spectra of neutral molecules, are dictated by the localization of the singly occupied 5 sigma orbital, adding a dimension of chemistry to the ionic NEXAFS technique.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2020
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-279214 (URN)10.1039/d0cp02207a (DOI)000552193500038 ()32643725 (PubMedID)2-s2.0-85088680676 (Scopus ID)
Note

QC 20200818

Available from: 2020-08-18 Created: 2020-08-18 Last updated: 2022-06-26Bibliographically approved
Lindblad, R., Kjellsson, L., Carvalho Couto, R., Timm, M., Bulow, C., Zamudio-Bayer, V., . . . Rubensson, J.-E. -. (2020). X-Ray Absorption Spectrum of the N-2(+) Molecular Ion. Physical Review Letters, 124(20), Article ID 203001.
Open this publication in new window or tab >>X-Ray Absorption Spectrum of the N-2(+) Molecular Ion
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2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 20, article id 203001Article in journal (Refereed) Published
Abstract [en]

The x-ray absorption spectrum of N-2(+) in the K-edge region has been measured by irradiation of ions stored in a cryogenic radio frequency ion trap with synchrotron radiation. We interpret the experimental results with the help of restricted active space multiconfiguration theory. Spectroscopic constants of the l sigma(-1 2)(u)Sigma(+)(u) state, and the two 1 sigma(-1)(u) 3 sigma(-1)(g) 1 pi(y) (II alpha)-I-2 states are determined from the measurements. The charge of the ground state together with spin coupling involving several open shells give rise to double excitations and configuration mixing, and a complete breakdown of the orbital picture for higher lying core-excited states.

Place, publisher, year, edition, pages
American Physical Society, 2020
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-275615 (URN)10.1103/PhysRevLett.124.203001 (DOI)000534179600006 ()32501042 (PubMedID)2-s2.0-85085842970 (Scopus ID)
Note

QC 20200608

Available from: 2020-06-08 Created: 2020-06-08 Last updated: 2024-03-18Bibliographically approved
Delcey, M. G., Sörensen, L. K., Vacher, M., Couto, R. C. & Lundberg, M. (2019). Efficient calculations of a large number of highly excited states for multiconfigurational wavefunctions. Journal of Computational Chemistry, 40(19), 1789-1799
Open this publication in new window or tab >>Efficient calculations of a large number of highly excited states for multiconfigurational wavefunctions
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2019 (English)In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 40, no 19, p. 1789-1799Article in journal (Refereed) Published
Abstract [en]

Electronically excited states play important roles in many chemical reactions and spectroscopic techniques. In quantum chemistry, a common technique to solve excited states is the multiroot Davidson algorithm, but it is not designed for processes like X-ray spectroscopy that involves hundreds of highly excited states. We show how the use of a restricted active space wavefunction together with a projection operator to remove low-lying electronic states offers an efficient way to reach single and double-core-hole states. Additionally, several improvements to the stability and efficiency of the configuration interaction (CI) algorithm for a large number of states are suggested. When applied to a series of transition metal complexes the new CI algorithm does not only resolve divergence issues but also leads to typical reduction in computational time by 70%, with the largest savings for small molecules and large active spaces. Together, the projection operator and the improved CI algorithm now make it possible to simulate a wide range of single- and two-photon spectroscopies.

Place, publisher, year, edition, pages
Wiley, 2019
Keywords
configuration interaction, excited states, X-ray spectroscopy, multiconfigurational wavefunction, computational cost
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-290056 (URN)10.1002/jcc.25832 (DOI)000470013600006 ()30938847 (PubMedID)2-s2.0-85063905506 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Olle Engkvists stiftelse
Note

QC 20210216

Available from: 2021-02-12 Created: 2021-02-12 Last updated: 2024-01-18Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-4020-0923

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