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34 results on '"Sørensen, Lasse Kragh"'

1. Transient spectroscopy from time-dependent electronic-structure theory without multipole expansions

Author

Aurbakken, Einar, Ofstad, Benedicte Sverdrup, Kristiansen, Håkon Emil, Schøyen, Øyvind Sigmundson, Kvaal, Simen, Sørensen, Lasse Kragh, Lindh, Roland, and Pedersen, Thomas Bondo

Subjects
Physics - Chemical Physics
Abstract

Based on the work done by an electromagnetic field on an atomic or molecular electronic system, a general gauge invariant formulation of transient absorption spectroscopy is presented within the semi-classical approximation. Avoiding multipole expansions, a computationally viable expression for the spectral response function is derived from the minimal-coupling Hamiltonian of an electronic system interacting with one or more laser pulses described by a source-free, enveloped electromagnetic vector potential. With a fixed-basis expansion of the electronic wave function, the computational cost of simulations of laser-driven electron dynamics beyond the dipole approximation is the same as simulations adopting the dipole approximation. We illustrate the theory by time-dependent configuration interaction and coupled-cluster simulations of core-level absorption and circular dichroism spectra.

Published
2023
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3. Transformation to a geminal basis and stationary conditions for the exact wave function therein

Author

Sørensen, Lasse Kragh

Subjects
Physics - Chemical Physics, Condensed Matter - Strongly Correlated Electrons, Physics - Computational Physics, Quantum Physics
Abstract

We show the transformation from a one-particle basis to a geminal basis, transformations between different geminal bases and demonstrate the Lie algebra of a geminal basis. From the basis transformations we express both the wave function and Hamiltonian in the geminal basis. The necessary and sufficient conditions of the exact wave function expanded in a geminal basis is shown to be a Brillouin theorem of geminals. The variational optimization of the geminals in the Antisymmetrized Geminal Power (AGP), Antisymmetrized Product of Geminals (APG) and the Full Geminal Product (FGP) wave function ans{\"a}tze are discussed. We show that using a geminal replacement operator to describe geminal rotations introduce both primary and secondary rotations. The secondary rotations rotate two geminals in the reference at the same time due to the composite boson nature of geminals. Due to the completeness of the FGP, where all possible geminal combinations are present, the FGP is exact. The number of parameters in the FGP scale exponentially with the number of particles, like the Full Configuration Interaction (FCI). Truncation in the FGP expansion could lead to compact representations of the wave function in the future since the reference function in the FGP is the APG wave function., Comment: 21 pages

Published
2019

4. Implementation of the exact semi-classical light-matter interaction - the easy way

Author

Sørensen, Lasse Kragh, Kieri, Emil, Srivastav, Shruti, Lundberg, Marcus, and Lindh, Roland

Subjects
Physics - Chemical Physics, Physics - Computational Physics
Abstract

We present an analytical and numerical solution of the calculation of the transition moments for the exact semi-classical light-matter interaction for wavefunctions expanded in a Gaussian basis. By a simple manipulation we show that the exact semi-classical light-matter interaction of a plane wave can be compared to a Fourier transformation of a Gaussian where analytical recursive formulas are well known and hence making the difficulty in the implementation of the exact semi-classical light-matter interaction comparable to the transition dipole. Since the evaluation of the analytical expression involves a new Gaussian we instead have chosen to evaluate the integrals using a standard Gau{\ss}-Hermite quadrature since this is faster. A brief discussion of the numerical advantages of the exact semi-classical light-matter interaction in comparison to the multipole expansion along with the unphysical interpretation of the multipole expansion is discussed. Numerical examples on [CuCl$_4$]$^{2-}$ to show that the usual features of the multipole expansion is immediately visible also for the exact semi-classical light-matter interaction and that this can be used to distinguish between symmetries. Calculation on [FeCl$_4$]$^{1-}$ is presented to demonstrate the better numerical stability with respect to the choice of basis set in comparison to the multipole expansion and finally Fe-O-Fe to show origin independence is a given for the exact operator. The implementation is freely available in OpenMolcas., Comment: 22 pages, 4 figures

Published
2018
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5. The Integral Screened Configuration Interaction Method

Author

Sørensen, Lasse Kragh, Bauch, Sebastian, and Madsen, Lars Bojer

Subjects
Physics - Chemical Physics, Physics - Atomic Physics, Physics - Computational Physics
Abstract

We present the formulation and implementation of the Integral-Screened Configuration-Interaction method (ISCI). The ISCI is a minimal-operational count integral-driven direct Configuration-Interaction (CI) method with a simple and rigorous integral screening (IS). With a novel derivation of the CI equations we show that the time consuming $\sigma$-vector calculation is separable up to an overall sign and that this separability can lead to a rigorous IS. The rigorous IS leads to linear scaling in the $\sigma$-vector step for large systems but can also lead to near linear scaling for smaller systems for the standard CISD, CISDT and CISDTQ methods, where the exponent for the scaling is 1.27, 1.48 and 1.98, respectively, even while retaining an accuracy of $10^{-14}$ or less in the energy. In the ISCI the non-relativistic CI problem can be broken into 42 generalized-matrix-vector products in the $\sigma$-vector calculation, which can be separately optimized. Due to the IS the ISCI can use dramatically larger orbital spaces combined with large CI expansions, on a single cpu, as compared with traditional CI methods. Further, it offers an intrinsic possibility for parallelization on modern computing architectures. We show examples of how IS leads to linear or near linear scaling with respect to the size of the simulation box in calculations on the Beryllium atom., Comment: 32 pages, 16 figures, 1 table

Published
2016

6. What do we approximate and what are the consequences in perturbation theory?

Author

Sørensen, Lasse Kragh, Lindh, Roland, and Lundberg, Marcus

Subjects
Physics - Chemical Physics, Physics - Computational Physics
Abstract

We present a discussion of the consequences in perturbation theory when an exact eigenfunctions and eigenvalues to to the zeroth order Hamiltonian $H_0$ cannot be found. Since the usual approximations such as projecting the wavefunction on to a finite basis set and restricting the particle interaction is a way of constructing an approximate zeroth order Hamiltonian $H_0'$ we will here argue that the exact eigenfunctions and eigenvalues are always found for $H_0'$. We will show that as long as the perturbative expansion does not depend on any intrinsic properties of $H_0$ but only on knowing the exact eigenfunctions and eigenvalues then any perturbative statement, such as origin independence intensities, will be true for any $H_0'$ provided that $H_0'$ has a spectrum. We will use this to show that the origin independence for the intensities is trivially fulfilled in the velocity gauge but also can be fulfilled exactly in the length gauge if an appropriate $H_0$ is chosen. Finally a small numerically demonstration of the origin dependence of the terms for the second-order intensities in both the length and velocity gauge is undertaking to numerically illustrate the theoretical statements., Comment: 13 pages, 3 figures

Published
2016

7. Correlation effects in strong-field ionization of heteronuclear diatomic molecules

Author

Larsson, Henrik R., Bauch, Sebastian, Sørensen, Lasse Kragh, and Bonitz, Michael

Subjects
Physics - Chemical Physics, Physics - Computational Physics, Quantum Physics
Abstract

We develop a time-dependent theory to investigate electron dynamics and photoionization processes of diatomic molecules interacting with strong laser fields including electron-electron correlation effects. We combine the recently formulated time-dependent generalized-active-space configuration interaction theory [D. Hochstuhl and M. Bonitz, Phys. Rev. A 86, 053424 (2012); S. Bauch, et al., Phys. Rev. A 90, 062508 (2014)] with a prolate spheroidal basis set including localized orbitals and continuum states to describe the bound electrons and the outgoing photoelectron. As an example, we study the strong-field ionization of the two-center four-electron lithium hydride molecule in different intensity regimes. By using single-cycle pulses, two orientations of the asymmetric heteronuclear molecule are investigated: Li-H, with the electrical field pointing from H to Li, and the opposite case of H-Li. The preferred orientation for ionization is determined and we find a transition from H-Li, for low intensity, to Li-H, for high intensity. The influence of electron correlations is studied at different levels of approximation, and we find a significant change in the preferred orientation. For certain intensity regimes, even an interchange of the preferred configuration is observed, relative to the uncorrelated simulations. Further insight is provided by detailed comparisons of photoelectron angular distributions with and without correlation effects taken into account.

Published
2015
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9. Time-dependent generalized-active-space configuration-interaction approach to photoionization dynamics of atoms and molecules

Author

Bauch, Sebastian, Sørensen, Lasse Kragh, and Madsen, Lars Bojer

Subjects
Quantum Physics, Physics - Chemical Physics
Abstract

We present a wave-function based method to solve the time-dependent many-electron Schr\"odinger equation (TDSE) with special emphasis on strong-field ionization phenomena. The theory builds on the configuration-interaction (CI) approach supplemented by the generalized-active-space (GAS) concept from quantum chemistry. The latter allows for a controllable reduction in the number of configurations in the CI expansion by imposing restrictions on the active orbital space. The method is similar to the recently formulated time-dependent restricted-active-space (TD-RAS) CI method [D. Hochstuhl, and M. Bonitz, Phys. Rev. A 86, 053424 (2012)]. We present details of our implementation and address convergence properties with respect to the active spaces and the associated account of electron correlation in both ground state and excitation scenarios. We apply the TD-GASCI theory to strong-field ionization of polar diatomic molecules and illustrate how the method allows us to uncover a strong correlation-induced shift of the preferred direction of emission of photoelectrons., Comment: 22 pages, 13 figures

Published
2014
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10. The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

Author

Fundación la Caixa, European Commission, Ministerio de Ciencia e Innovación (España), Department of Energy (US), Swiss National Science Foundation, Ministero dell'Istruzione, dell'Università e della Ricerca, Carl Trygger Foundation, Royal Society (UK), Independent Research Fund Denmark, German Research Foundation, Generalitat de Catalunya, Olle Engkvist Foundation, National Centre for Research and Development (Poland), National Science Foundation (US), Academy of Finland, Knut and Alice Wallenberg Foundation, Swedish Research Council, Université de Nantes, Japan Society for the Promotion of Science, Università degli Studi di Siena, Novo Nordisk Foundation, Argonne National Laboratory (US), National University of Singapore, Air Force Office of Scientific Research (US), Linköping University, Centre National de la Recherche Scientifique (France), Li Manni, Giovanni [0000-0002-3666-3880], Fdez Galván, Ignacio [0000-0002-0684-7689], #NODATA#, Aleotti, Flavia [0000-0002-7176-5305], Aquilante, Francesco [0000-0003-4422-3938], Autschbach, Jochen [0000-0001-9392-877X], Avagliano, Davide [0000-0001-5539-9731], Baiardi, Alberto [0000-0001-9112-8664], Bao, Jie J. [0000-0003-0197-3405], Battaglia, Stefano [0000-0002-5082-2681], Blanco-González, Alejandro [0000-0001-7379-2588], Bokarev, Sergey I. [0000-0003-0779-5013], Broer, Ria [0000-0002-5437-9509], Cacciari, Roberto [0000-0001-8290-4297], Calio, Paul B. [0000-0001-8385-2628], Carlson, Rebecca K. [0000-0002-1710-5816], Carvalho Couto, Rafael [0000-0003-4020-0923], Cerdán, L. [0000-0002-7174-2453], Chibotaru, Liviu F. [0000-0003-1556-0812], Chilton, Nicholas F. [0000-0002-8604-0171], Church, Jonathan Richard [0000-0001-5986-1305], Conti, Irene [0000-0001-7982-4480], Coriani, Sonia [0000-0002-4487-897X], Cuéllar-Zuquin, Juliana [0000-0002-0127-579X], Daoud, Razan E. [0000-0001-7034-0770], Dattani, Nike [0000-0001-5667-3632], Decleva, Piero [0000-0002-7322-887X], de Graaf, Coen [0000-0001-8114-6658], Delcey, Mickaël G. [0000-0001-9883-3569], De Vico, Luca [0000-0002-2821-5711], Dobrautz, Werner [0000-0001-6479-1874], Dong, Sijia S. [0000-0001-8182-6522], Feng, Rulin [0000-0002-9812-3804], Ferré, Nicolas [0000-0002-5583-8834], Filatov Gulak, Michael [0000-0002-1541-739X], Gagliardi, Laura [0000-0001-5227-1396], Garavelli, Marco [0000-0002-0796-289X], González, Leticia [0000-0001-5112-794X], Guo, Meiyuan [0000-0003-2474-6264], Hennefarth, Matthew R. [0000-0002-6601-2253], Hermes, Matthew R. [0000-0001-7807-2950], Huix-Rotllant, Miquel [0000-0002-2131-7328], Jaiswal, Vishal Kumar [0000-0002-5090-7984], Kaliakin, Danil S. [0000-0002-9354-8248], King, Daniel S. [0000-0003-0208-5274], Larsson, Ernst D. [0000-0001-7655-2993], Lehtola, Susi [0000-0001-6296-8103], Lepetit, Marie-Bernadette [0000-0001-8730-4282], Lischka, Hans [0000-0002-5656-3975], Lundberg, Marcus [0000-0002-1312-1202], Mai, Sebastian [0000-0001-5327-8880], Marquetand, Philipp [0000-0002-8711-1533], Merritt, Isabella C. D. [0000-0002-7965-7798], Nenov, Artur [0000-0003-3071-5341], Nguyen, Vu Ha Anh [0000-0002-4177-0656], Nishimoto, Yoshio [0000-0001-5581-4712], Oakley, Meagan S. [0000-0001-5072-7572], Olivucci, Massimo [0000-0002-8247-209X], Oppel, Markus [0000-0001-6363-2310], Padula, Daniele [0000-0002-7171-7928], Pandharkar, Riddhish [0000-0003-4086-4308], Phung, Quan Manh [0000-0001-8205-5328], Plasser, Felix [0000-0003-0751-148X], Reiher, Markus [0000-0002-9508-1565], Rivalta, Ivan [0000-0002-1208-602X], Roca-Sanjuán, Daniel [0000-0001-6495-2770], Romig, Thies [0000-0002-9424-2398], Safari, Arta Anushirwan [0000-0003-4511-8902], Sánchez-Mansilla, Aitor [0000-0002-2601-190X], Sand, Andrew M. [0000-0002-7166-2066], Schapiro, Igor [0000-0001-8536-6869], Scott, Thais R. [0000-0002-5746-5517], Segarra-Martí, Javier [0000-0002-2076-3406], Segatta, Francesco [0000-0003-4150-6676], Sergentu, Dumitru-Claudiu [0000-0001-6570-5245], Shepard, Ron [0000-0002-0272-0824], Shu, Yinan [0000-0002-8371-0221], Sørensen, Lasse Kragh [0000-0002-1931-1867], Tenorio, Bruno Nunes Cabral [0000-0002-9702-998X], Truhlar, Donald G. [0000-0002-7742-7294], Ungur, Liviu [0000-0001-5015-4225], Vacher, Morgane [0000-0001-9418-6579], Veryazov, Valera [0000-0002-0172-7047], Li Manni, Giovanni, Fdez Galván, Ignacio, Alavi, Ali, Aleotti, Flavia, Aquilante, Francesco, Autschbach, Jochen, Avagliano, Davide, Baiardi, Alberto, Bao, Jie J., Battaglia, Stefano, Birnoschi, Letitia, Blanco-González, Alejandro, Bokarev, Sergey I., Broer, Ria, Cacciari, Roberto, Calio, Paul B., Carlson, Rebecca K., Carvalho Couto, Rafael, Cerdán, L., Chibotaru, Liviu F., Chilton, Nicholas F., Church, Jonathan Richard, Conti, Irene, Coriani, Sonia, Cuéllar-Zuquin, Juliana, Daoud, Razan E., Dattani, Nike, Decleva, Piero, de Graaf, Coen, Delcey, Mickaël G., De Vico, Luca, Dobrautz, Werner, Dong, Sijia S., Feng, Rulin, Ferré, Nicolas, Filatov Gulak, Michael, Gagliardi, Laura, Garavelli, Marco, González, Leticia, Guan, Yafu, Guo, Meiyuan, Hennefarth, Matthew R., Hermes, Matthew R., Hoyer, Chad E., Huix-Rotllant, Miquel, Jaiswal, Vishal Kumar, Kaiser, Andy, Kaliakin, Danil S., Khamesian, Marjan, King, Daniel S., Kochetov, Vladislav, Krośnicki, Marek, Kumaar, Arpit Arun, Larsson, Ernst D., Lehtola, Susi, Lepetit, Marie-Bernadette, Lischka, Hans, López Ríos, Pablo, Lundberg, Marcus, Ma, Dongxia, Mai, Sebastian, Marquetand, Philipp, Merritt, Isabella C. D., Montorsi, Francesco, Mörchen, Maximilian, Nenov, Artur, Nguyen, Vu Ha Anh, Nishimoto, Yoshio, Oakley, Meagan S., Olivucci, Massimo, Oppel, Markus, Padula, Daniele, Pandharkar, Riddhish, Phung, Quan Manh, Plasser, Felix, Raggi, Gerardo, Rebolini, Elisa, Reiher, Markus, Rivalta, Ivan, Roca-Sanjuán, Daniel, Romig, Thies, Safari, Arta Anushirwan, Sánchez-Mansilla, Aitor, Sand, Andrew M., Schapiro, Igor, Scott, Thais R., Segarra-Martí, Javier, Segatta, Francesco, Sergentu, Dumitru-Claudiu, Sharma, Prachi, Shepard, Ron, Shu, Yinan, Staab, Jakob K., Straatsma, Tjerk P., Sørensen, Lasse Kragh, Tenorio, Bruno Nunes Cabral, Truhlar, Donald G., Ungur, Liviu, Vacher, Morgane, Veryazov, Valera, Voß, Torben Arne, Weser, Oskar, Wu, Dihua, Yang, Xuchun, Yarkony, David, Zhou, Chen, Zobel, J Patrick, Lindh, Roland, Fundación la Caixa, European Commission, Ministerio de Ciencia e Innovación (España), Department of Energy (US), Swiss National Science Foundation, Ministero dell'Istruzione, dell'Università e della Ricerca, Carl Trygger Foundation, Royal Society (UK), Independent Research Fund Denmark, German Research Foundation, Generalitat de Catalunya, Olle Engkvist Foundation, National Centre for Research and Development (Poland), National Science Foundation (US), Academy of Finland, Knut and Alice Wallenberg Foundation, Swedish Research Council, Université de Nantes, Japan Society for the Promotion of Science, Università degli Studi di Siena, Novo Nordisk Foundation, Argonne National Laboratory (US), National University of Singapore, Air Force Office of Scientific Research (US), Linköping University, Centre National de la Recherche Scientifique (France), Li Manni, Giovanni [0000-0002-3666-3880], Fdez Galván, Ignacio [0000-0002-0684-7689], #NODATA#, Aleotti, Flavia [0000-0002-7176-5305], Aquilante, Francesco [0000-0003-4422-3938], Autschbach, Jochen [0000-0001-9392-877X], Avagliano, Davide [0000-0001-5539-9731], Baiardi, Alberto [0000-0001-9112-8664], Bao, Jie J. [0000-0003-0197-3405], Battaglia, Stefano [0000-0002-5082-2681], Blanco-González, Alejandro [0000-0001-7379-2588], Bokarev, Sergey I. [0000-0003-0779-5013], Broer, Ria [0000-0002-5437-9509], Cacciari, Roberto [0000-0001-8290-4297], Calio, Paul B. [0000-0001-8385-2628], Carlson, Rebecca K. [0000-0002-1710-5816], Carvalho Couto, Rafael [0000-0003-4020-0923], Cerdán, L. [0000-0002-7174-2453], Chibotaru, Liviu F. [0000-0003-1556-0812], Chilton, Nicholas F. [0000-0002-8604-0171], Church, Jonathan Richard [0000-0001-5986-1305], Conti, Irene [0000-0001-7982-4480], Coriani, Sonia [0000-0002-4487-897X], Cuéllar-Zuquin, Juliana [0000-0002-0127-579X], Daoud, Razan E. [0000-0001-7034-0770], Dattani, Nike [0000-0001-5667-3632], Decleva, Piero [0000-0002-7322-887X], de Graaf, Coen [0000-0001-8114-6658], Delcey, Mickaël G. [0000-0001-9883-3569], De Vico, Luca [0000-0002-2821-5711], Dobrautz, Werner [0000-0001-6479-1874], Dong, Sijia S. [0000-0001-8182-6522], Feng, Rulin [0000-0002-9812-3804], Ferré, Nicolas [0000-0002-5583-8834], Filatov Gulak, Michael [0000-0002-1541-739X], Gagliardi, Laura [0000-0001-5227-1396], Garavelli, Marco [0000-0002-0796-289X], González, Leticia [0000-0001-5112-794X], Guo, Meiyuan [0000-0003-2474-6264], Hennefarth, Matthew R. [0000-0002-6601-2253], Hermes, Matthew R. [0000-0001-7807-2950], Huix-Rotllant, Miquel [0000-0002-2131-7328], Jaiswal, Vishal Kumar [0000-0002-5090-7984], Kaliakin, Danil S. [0000-0002-9354-8248], King, Daniel S. [0000-0003-0208-5274], Larsson, Ernst D. [0000-0001-7655-2993], Lehtola, Susi [0000-0001-6296-8103], Lepetit, Marie-Bernadette [0000-0001-8730-4282], Lischka, Hans [0000-0002-5656-3975], Lundberg, Marcus [0000-0002-1312-1202], Mai, Sebastian [0000-0001-5327-8880], Marquetand, Philipp [0000-0002-8711-1533], Merritt, Isabella C. D. [0000-0002-7965-7798], Nenov, Artur [0000-0003-3071-5341], Nguyen, Vu Ha Anh [0000-0002-4177-0656], Nishimoto, Yoshio [0000-0001-5581-4712], Oakley, Meagan S. [0000-0001-5072-7572], Olivucci, Massimo [0000-0002-8247-209X], Oppel, Markus [0000-0001-6363-2310], Padula, Daniele [0000-0002-7171-7928], Pandharkar, Riddhish [0000-0003-4086-4308], Phung, Quan Manh [0000-0001-8205-5328], Plasser, Felix [0000-0003-0751-148X], Reiher, Markus [0000-0002-9508-1565], Rivalta, Ivan [0000-0002-1208-602X], Roca-Sanjuán, Daniel [0000-0001-6495-2770], Romig, Thies [0000-0002-9424-2398], Safari, Arta Anushirwan [0000-0003-4511-8902], Sánchez-Mansilla, Aitor [0000-0002-2601-190X], Sand, Andrew M. [0000-0002-7166-2066], Schapiro, Igor [0000-0001-8536-6869], Scott, Thais R. [0000-0002-5746-5517], Segarra-Martí, Javier [0000-0002-2076-3406], Segatta, Francesco [0000-0003-4150-6676], Sergentu, Dumitru-Claudiu [0000-0001-6570-5245], Shepard, Ron [0000-0002-0272-0824], Shu, Yinan [0000-0002-8371-0221], Sørensen, Lasse Kragh [0000-0002-1931-1867], Tenorio, Bruno Nunes Cabral [0000-0002-9702-998X], Truhlar, Donald G. [0000-0002-7742-7294], Ungur, Liviu [0000-0001-5015-4225], Vacher, Morgane [0000-0001-9418-6579], Veryazov, Valera [0000-0002-0172-7047], Li Manni, Giovanni, Fdez Galván, Ignacio, Alavi, Ali, Aleotti, Flavia, Aquilante, Francesco, Autschbach, Jochen, Avagliano, Davide, Baiardi, Alberto, Bao, Jie J., Battaglia, Stefano, Birnoschi, Letitia, Blanco-González, Alejandro, Bokarev, Sergey I., Broer, Ria, Cacciari, Roberto, Calio, Paul B., Carlson, Rebecca K., Carvalho Couto, Rafael, Cerdán, L., Chibotaru, Liviu F., Chilton, Nicholas F., Church, Jonathan Richard, Conti, Irene, Coriani, Sonia, Cuéllar-Zuquin, Juliana, Daoud, Razan E., Dattani, Nike, Decleva, Piero, de Graaf, Coen, Delcey, Mickaël G., De Vico, Luca, Dobrautz, Werner, Dong, Sijia S., Feng, Rulin, Ferré, Nicolas, Filatov Gulak, Michael, Gagliardi, Laura, Garavelli, Marco, González, Leticia, Guan, Yafu, Guo, Meiyuan, Hennefarth, Matthew R., Hermes, Matthew R., Hoyer, Chad E., Huix-Rotllant, Miquel, Jaiswal, Vishal Kumar, Kaiser, Andy, Kaliakin, Danil S., Khamesian, Marjan, King, Daniel S., Kochetov, Vladislav, Krośnicki, Marek, Kumaar, Arpit Arun, Larsson, Ernst D., Lehtola, Susi, Lepetit, Marie-Bernadette, Lischka, Hans, López Ríos, Pablo, Lundberg, Marcus, Ma, Dongxia, Mai, Sebastian, Marquetand, Philipp, Merritt, Isabella C. D., Montorsi, Francesco, Mörchen, Maximilian, Nenov, Artur, Nguyen, Vu Ha Anh, Nishimoto, Yoshio, Oakley, Meagan S., Olivucci, Massimo, Oppel, Markus, Padula, Daniele, Pandharkar, Riddhish, Phung, Quan Manh, Plasser, Felix, Raggi, Gerardo, Rebolini, Elisa, Reiher, Markus, Rivalta, Ivan, Roca-Sanjuán, Daniel, Romig, Thies, Safari, Arta Anushirwan, Sánchez-Mansilla, Aitor, Sand, Andrew M., Schapiro, Igor, Scott, Thais R., Segarra-Martí, Javier, Segatta, Francesco, Sergentu, Dumitru-Claudiu, Sharma, Prachi, Shepard, Ron, Shu, Yinan, Staab, Jakob K., Straatsma, Tjerk P., Sørensen, Lasse Kragh, Tenorio, Bruno Nunes Cabral, Truhlar, Donald G., Ungur, Liviu, Vacher, Morgane, Veryazov, Valera, Voß, Torben Arne, Weser, Oskar, Wu, Dihua, Yang, Xuchun, Yarkony, David, Zhou, Chen, Zobel, J Patrick, and Lindh, Roland

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.

Published
2023

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

Author

Li Manni, Giovanni, primary, Fdez. Galván, Ignacio, additional, Alavi, Ali, additional, Aleotti, Flavia, additional, Aquilante, Francesco, additional, Autschbach, Jochen, additional, Avagliano, Davide, additional, Baiardi, Alberto, additional, Bao, Jie J., additional, Battaglia, Stefano, additional, Birnoschi, Letitia, additional, Blanco-González, Alejandro, additional, Bokarev, Sergey I., additional, Broer, Ria, additional, Cacciari, Roberto, additional, Calio, Paul B., additional, Carlson, Rebecca K., additional, Carvalho Couto, Rafael, additional, Cerdán, Luis, additional, Chibotaru, Liviu F., additional, Chilton, Nicholas F., additional, Church, Jonathan Richard, additional, Conti, Irene, additional, Coriani, Sonia, additional, Cuéllar-Zuquin, Juliana, additional, Daoud, Razan E., additional, Dattani, Nike, additional, Decleva, Piero, additional, de Graaf, Coen, additional, Delcey, Mickaël G., additional, De Vico, Luca, additional, Dobrautz, Werner, additional, Dong, Sijia S., additional, Feng, Rulin, additional, Ferré, Nicolas, additional, Filatov(Gulak), Michael, additional, Gagliardi, Laura, additional, Garavelli, Marco, additional, González, Leticia, additional, Guan, Yafu, additional, Guo, Meiyuan, additional, Hennefarth, Matthew R., additional, Hermes, Matthew R., additional, Hoyer, Chad E., additional, Huix-Rotllant, Miquel, additional, Jaiswal, Vishal Kumar, additional, Kaiser, Andy, additional, Kaliakin, Danil S., additional, Khamesian, Marjan, additional, King, Daniel S., additional, Kochetov, Vladislav, additional, Krośnicki, Marek, additional, Kumaar, Arpit Arun, additional, Larsson, Ernst D., additional, Lehtola, Susi, additional, Lepetit, Marie-Bernadette, additional, Lischka, Hans, additional, López Ríos, Pablo, additional, Lundberg, Marcus, additional, Ma, Dongxia, additional, Mai, Sebastian, additional, Marquetand, Philipp, additional, Merritt, Isabella C. D., additional, Montorsi, Francesco, additional, Mörchen, Maximilian, additional, Nenov, Artur, additional, Nguyen, Vu Ha Anh, additional, Nishimoto, Yoshio, additional, Oakley, Meagan S., additional, Olivucci, Massimo, additional, Oppel, Markus, additional, Padula, Daniele, additional, Pandharkar, Riddhish, additional, Phung, Quan Manh, additional, Plasser, Felix, additional, Raggi, Gerardo, additional, Rebolini, Elisa, additional, Reiher, Markus, additional, Rivalta, Ivan, additional, Roca-Sanjuán, Daniel, additional, Romig, Thies, additional, Safari, Arta Anushirwan, additional, Sánchez-Mansilla, Aitor, additional, Sand, Andrew M., additional, Schapiro, Igor, additional, Scott, Thais R., additional, Segarra-Martí, Javier, additional, Segatta, Francesco, additional, Sergentu, Dumitru-Claudiu, additional, Sharma, Prachi, additional, Shepard, Ron, additional, Shu, Yinan, additional, Staab, Jakob K., additional, Straatsma, Tjerk P., additional, Sørensen, Lasse Kragh, additional, Tenorio, Bruno Nunes Cabral, additional, Truhlar, Donald G., additional, Ungur, Liviu, additional, Vacher, Morgane, additional, Veryazov, Valera, additional, Voß, Torben Arne, additional, Weser, Oskar, additional, Wu, Dihua, additional, Yang, Xuchun, additional, Yarkony, David, additional, Zhou, Chen, additional, Zobel, J. Patrick, additional, and Lindh, Roland, additional

Published
2023
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14. The OpenMolcas Web:A Community-Driven Approach to Advancing Computational Chemistry

Author

Li Manni, Giovanni, Fdez. Galván, Ignacio, Alavi, Ali, Aleotti, Flavia, Aquilante, Francesco, Autschbach, Jochen, Avagliano, Davide, Baiardi, Alberto, Bao, Jie J., Battaglia, Stefano, Birnoschi, Letitia, Blanco-González, Alejandro, Bokarev, Sergey I., Broer, Ria, Cacciari, Roberto, Calio, Paul B., Carlson, Rebecca K., Carvalho Couto, Rafael, Cerdán, Luis, Chibotaru, Liviu F., Chilton, Nicholas F., Church, Jonathan Richard, Conti, Irene, Coriani, Sonia, Cuéllar-Zuquin, Juliana, Daoud, Razan E., Dattani, Nike, Decleva, Piero, de Graaf, Coen, Delcey, Mickaël G., De Vico, Luca, Dobrautz, Werner, Dong, Sijia S., Feng, Rulin, Ferré, Nicolas, Filatov(Gulak), Michael, Gagliardi, Laura, Garavelli, Marco, González, Leticia, Guan, Yafu, Guo, Meiyuan, Hennefarth, Matthew R., Hermes, Matthew R., Hoyer, Chad E., Huix-Rotllant, Miquel, Jaiswal, Vishal Kumar, Kaiser, Andy, Kaliakin, Danil S., Khamesian, Marjan, King, Daniel S., Kochetov, Vladislav, Krośnicki, Marek, Kumaar, Arpit Arun, Larsson, Ernst D., Lehtola, Susi, Lepetit, Marie Bernadette, Lischka, Hans, López Ríos, Pablo, Lundberg, Marcus, Ma, Dongxia, Mai, Sebastian, Marquetand, Philipp, Merritt, Isabella C.D., Montorsi, Francesco, Mörchen, Maximilian, Nenov, Artur, Nguyen, Vu Ha Anh, Nishimoto, Yoshio, Oakley, Meagan S., Olivucci, Massimo, Oppel, Markus, Padula, Daniele, Pandharkar, Riddhish, Phung, Quan Manh, Plasser, Felix, Raggi, Gerardo, Rebolini, Elisa, Reiher, Markus, Rivalta, Ivan, Roca-Sanjuán, Daniel, Romig, Thies, Safari, Arta Anushirwan, Sánchez-Mansilla, Aitor, Sand, Andrew M., Schapiro, Igor, Scott, Thais R., Segarra-Martí, Javier, Segatta, Francesco, Sergentu, Dumitru Claudiu, Sharma, Prachi, Shepard, Ron, Shu, Yinan, Staab, Jakob K., Straatsma, Tjerk P., Sørensen, Lasse Kragh, Tenorio, Bruno Nunes Cabral, Truhlar, Donald G., Ungur, Liviu, Vacher, Morgane, Veryazov, Valera, Voß, Torben Arne, Weser, Oskar, Wu, Dihua, Yang, Xuchun, Yarkony, David, Zhou, Chen, Zobel, J. Patrick, Lindh, Roland, Li Manni, Giovanni, Fdez. Galván, Ignacio, Alavi, Ali, Aleotti, Flavia, Aquilante, Francesco, Autschbach, Jochen, Avagliano, Davide, Baiardi, Alberto, Bao, Jie J., Battaglia, Stefano, Birnoschi, Letitia, Blanco-González, Alejandro, Bokarev, Sergey I., Broer, Ria, Cacciari, Roberto, Calio, Paul B., Carlson, Rebecca K., Carvalho Couto, Rafael, Cerdán, Luis, Chibotaru, Liviu F., Chilton, Nicholas F., Church, Jonathan Richard, Conti, Irene, Coriani, Sonia, Cuéllar-Zuquin, Juliana, Daoud, Razan E., Dattani, Nike, Decleva, Piero, de Graaf, Coen, Delcey, Mickaël G., De Vico, Luca, Dobrautz, Werner, Dong, Sijia S., Feng, Rulin, Ferré, Nicolas, Filatov(Gulak), Michael, Gagliardi, Laura, Garavelli, Marco, González, Leticia, Guan, Yafu, Guo, Meiyuan, Hennefarth, Matthew R., Hermes, Matthew R., Hoyer, Chad E., Huix-Rotllant, Miquel, Jaiswal, Vishal Kumar, Kaiser, Andy, Kaliakin, Danil S., Khamesian, Marjan, King, Daniel S., Kochetov, Vladislav, Krośnicki, Marek, Kumaar, Arpit Arun, Larsson, Ernst D., Lehtola, Susi, Lepetit, Marie Bernadette, Lischka, Hans, López Ríos, Pablo, Lundberg, Marcus, Ma, Dongxia, Mai, Sebastian, Marquetand, Philipp, Merritt, Isabella C.D., Montorsi, Francesco, Mörchen, Maximilian, Nenov, Artur, Nguyen, Vu Ha Anh, Nishimoto, Yoshio, Oakley, Meagan S., Olivucci, Massimo, Oppel, Markus, Padula, Daniele, Pandharkar, Riddhish, Phung, Quan Manh, Plasser, Felix, Raggi, Gerardo, Rebolini, Elisa, Reiher, Markus, Rivalta, Ivan, Roca-Sanjuán, Daniel, Romig, Thies, Safari, Arta Anushirwan, Sánchez-Mansilla, Aitor, Sand, Andrew M., Schapiro, Igor, Scott, Thais R., Segarra-Martí, Javier, Segatta, Francesco, Sergentu, Dumitru Claudiu, Sharma, Prachi, Shepard, Ron, Shu, Yinan, Staab, Jakob K., Straatsma, Tjerk P., Sørensen, Lasse Kragh, Tenorio, Bruno Nunes Cabral, Truhlar, Donald G., Ungur, Liviu, Vacher, Morgane, Veryazov, Valera, Voß, Torben Arne, Weser, Oskar, Wu, Dihua, Yang, Xuchun, Yarkony, David, Zhou, Chen, Zobel, J. Patrick, and Lindh, Roland

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.

Published
2023

15. Exact semi-classical light–matter interaction operator applied to two-photon processes with strong relativistic effects.

Author

Delcey, Mickaël G., Couto, Rafael Carvalho, Sørensen, Lasse Kragh, Fdez. Galván, Ignacio, Guo, Meiyuan, Lindh, Roland, and Lundberg, Marcus

Subjects
INELASTIC scattering, X-ray scattering, MAGNITUDE (Mathematics), PHOTON scattering, ENERGY level transitions, PHOTONS, WAVELENGTHS
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. [ABSTRACT FROM AUTHOR]

Published
2020
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16. Setting the stage for theoretical x-ray spectra of the H2S molecule with multi-configurational quantum chemical calculations of the energy landscape.

Author

Ertan, Emelie, Lundberg, Marcus, Sørensen, Lasse Kragh, and Odelius, Michael

Subjects
CHEMICAL energy, MOLECULAR spectra, POTENTIAL energy surfaces, MOLECULAR orbitals, X-ray spectroscopy, X-ray spectra
Abstract

In the H2S molecule, the interplay between different core levels can be investigated in great detail in relation to x-ray spectroscopy, which requires a theory for interpretation. Hence, valence and core excitations into the two antibonding molecular orbitals of the H2S molecule have been calculated within a multi-configurational wave function framework. Scanning along the S–H stretching coordinates, we derive potential energy surfaces and transition dipole moments involving the ground state and core and valence excited states. Both valence excitations and the S1s−1 and S2p−1 core excitations show pairs of dissociative and bound electronic states. These pairs of states are nearly degenerate in H2S at the ground state geometry. The close degeneracy together with conical intersections makes H2S an interesting target for x-ray spectroscopy involving ultra-fast dissociation influenced by non-adiabatic transitions and interference. For future investigations with x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), it is valuable to compare H2S with the water molecule, which exhibits state-selective gating to different vibrational modes [R. C. Couto et al., Nat. Commun. 8, 14165 (2017)] in its well-separated O1s−1 core excited states. The dense manifolds of the S2p−1 core excited states will complicate the analysis of Kα edge RIXS, but dynamical effects could be evaluated through detuning and by comparing with L edge XAS. In L edge RIXS, the dynamical effects will be more pronounced due to the longer lifetime of the S2p−1 core excited states compared to the S1s−1 core excited states. [ABSTRACT FROM AUTHOR]

Published
2020
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17. The minimum parameterization of the wave function for the many-body electronic Schr\'odinger equation. Theory and ansatz

Author

Sørensen, Lasse Kragh

Subjects
Condensed Matter - Strongly Correlated Electrons, Quantum Physics, Physics - Chemical Physics, Physics - Computational Physics
Abstract

The minimum parameterization of the wave function is derived for the time-independent many-body problem. In this parameterization all electrons and electron pairs are indistinguishable which eliminates the exponential scaling with the number of particles plaguing all other correlation methods. An exponential scaling shown to stem from the expansion of the wave function in one-particle basis sets. It is demonstrated that using a geminal basis with a skew-symmetric orthogonal coefficient matrix, which fulfill a Lie algebra, the parameterization of the exact wave function becomes independent of the number of particles and only scale quadratic with the number of basis functions in the optimized basis and quartic in an arbitrary basis. The resulting antisymmetrized geminal power wave function is shown to fulfill the necessary and sufficient conditions for the exact wave function, treat all electrons and electron pairs as indistinguishable and be the most compact representation of the exact wave function possible. The number of parameters in the antisymmetrized geminal power wave function is exactly the same number of parameters as in the two-particle reduced density matrix thereby showing that these representations are equivalent just like the representations for a one-particle Hamiltonian. A detailed discussion of how the most compact wave function can be derived in general is also presented along with different geminal ans\"atze and sufficient closure relations. Due to the breaking of the scaling wall for the exact wave function it is expected that, if a general set of constraints can be found, even systems of biological relevance can be treated exactly in the future., Comment: 19 pages

Published
2019

18. Spectroscopy of linear and circular polarized ligth with the exact semiclassical light–matter interaction

Author

Khamesian, Marjan, Fernández Galván, Ignacio, Delcey, Mickael G, Sørensen, Lasse Kragh, Lindh, Roland, Khamesian, Marjan, Fernández Galván, Ignacio, Delcey, Mickael G, Sørensen, Lasse Kragh, and Lindh, Roland

Abstract

We present the theory and the analytical and numerical solution for the calculation of the oscillator and rotatory strengths of molecular systems using a state-specific formalism. For a start, this is done in the context of the exact semiclassical light–matter interaction in association with electronic wave functions expanded in a Gaussian basis. The reader is guided through the standard approximations of the field, e.g., the use of commutators, truncation of Taylor expansions, and the implications of these are discussed in parallel. Expressions for the isotropically averaged values are derived, recovering the isotropic oscillator strength in terms of the transition electric-dipole moment, and the isotropic rotatory strength in terms of the transition electric-dipole and magnetic-dipole moments. This chapter gives a detailed description of the computation of the integrals over the plane wave in association with Gaussian one-particle basis sets. Finally, a brief description is given of how the computed oscillator and rotatory strengths are related to the quantities commonly used and discussed in experimental studies.

Published
2019
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20. OpenMolcas : From Source Code to Insight

Author

Galván, Ignacio Fdez., Vacher, Morgane, Alavi, Ali, Angeli, Celestino, Aquilante, Francesco, Autschbach, Jochen, Bao, Jie J., Bokarev, Sergey I., Bogdanov, Nikolay A., Carlson, Rebecca K., Chibotaru, Liviu F., Creutzberg, Joel, Dattani, Nike, Delcey, Mickaël G., Dong, Sijia S., Dreuw, Andreas, Freitag, Leon, Manuel Frutos, Luis, Gagliardi, Laura, Gendron, Frédéric, Giussani, Angelo, González, Leticia, Grell, Gilbert, Guo, Meiyuan, Hoyer, Chad E., Johansson, Marcus, Keller, Sebastian, Knecht, Stefan, Kovačević, Goran, Källman, Erik, Li Manni, Giovanni, Lundberg, Marcus, Ma, Yingjin, Mai, Sebastian, Malhado, João Pedro, Malmqvist, Per Åke, Marquetand, Philipp, Mewes, Stefanie A., Norell, Jesper, Olivucci, Massimo, Oppel, Markus, Quan, Manh, Pierloot, Kristine, Plasser, Felix, Reiher, Markus, Sand, Andrew M., Schapiro, Igor, Sharma, Prachi, Stein, Christopher J., Sørensen, Lasse Kragh, Truhlar, Donald G., Ugandi, Mihkel, Ungur, Liviu, Valentini, Alessio, Vancoillie, Steven, Veryazov, Valera, Weser, Oskar, Wesołowski, Tomasz A., Widmark, Per-Olof, Wouters, Sebastian, Zech, Alexander, Zobel, J. Patrick, Lindh, Roland, Galván, Ignacio Fdez., Vacher, Morgane, Alavi, Ali, Angeli, Celestino, Aquilante, Francesco, Autschbach, Jochen, Bao, Jie J., Bokarev, Sergey I., Bogdanov, Nikolay A., Carlson, Rebecca K., Chibotaru, Liviu F., Creutzberg, Joel, Dattani, Nike, Delcey, Mickaël G., Dong, Sijia S., Dreuw, Andreas, Freitag, Leon, Manuel Frutos, Luis, Gagliardi, Laura, Gendron, Frédéric, Giussani, Angelo, González, Leticia, Grell, Gilbert, Guo, Meiyuan, Hoyer, Chad E., Johansson, Marcus, Keller, Sebastian, Knecht, Stefan, Kovačević, Goran, Källman, Erik, Li Manni, Giovanni, Lundberg, Marcus, Ma, Yingjin, Mai, Sebastian, Malhado, João Pedro, Malmqvist, Per Åke, Marquetand, Philipp, Mewes, Stefanie A., Norell, Jesper, Olivucci, Massimo, Oppel, Markus, Quan, Manh, Pierloot, Kristine, Plasser, Felix, Reiher, Markus, Sand, Andrew M., Schapiro, Igor, Sharma, Prachi, Stein, Christopher J., Sørensen, Lasse Kragh, Truhlar, Donald G., Ugandi, Mihkel, Ungur, Liviu, Valentini, Alessio, Vancoillie, Steven, Veryazov, Valera, Weser, Oskar, Wesołowski, Tomasz A., Widmark, Per-Olof, Wouters, Sebastian, Zech, Alexander, Zobel, J. Patrick, and Lindh, Roland

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.

Published
2019
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21. OpenMolcas: From Source Code to Insight

Author

Fdez. Galván, Ignacio, primary, Vacher, Morgane, additional, Alavi, Ali, additional, Angeli, Celestino, additional, Aquilante, Francesco, additional, Autschbach, Jochen, additional, Bao, Jie J., additional, Bokarev, Sergey I., additional, Bogdanov, Nikolay A., additional, Carlson, Rebecca K., additional, Chibotaru, Liviu F., additional, Creutzberg, Joel, additional, Dattani, Nike, additional, Delcey, Mickaël G., additional, Dong, Sijia S., additional, Dreuw, Andreas, additional, Freitag, Leon, additional, Frutos, Luis Manuel, additional, Gagliardi, Laura, additional, Gendron, Frédéric, additional, Giussani, Angelo, additional, González, Leticia, additional, Grell, Gilbert, additional, Guo, Meiyuan, additional, Hoyer, Chad E., additional, Johansson, Marcus, additional, Keller, Sebastian, additional, Knecht, Stefan, additional, Kovačević, Goran, additional, Källman, Erik, additional, Li Manni, Giovanni, additional, Lundberg, Marcus, additional, Ma, Yingjin, additional, Mai, Sebastian, additional, Malhado, João Pedro, additional, Malmqvist, Per Åke, additional, Marquetand, Philipp, additional, Mewes, Stefanie A., additional, Norell, Jesper, additional, Olivucci, Massimo, additional, Oppel, Markus, additional, Phung, Quan Manh, additional, Pierloot, Kristine, additional, Plasser, Felix, additional, Reiher, Markus, additional, Sand, Andrew M., additional, Schapiro, Igor, additional, Sharma, Prachi, additional, Stein, Christopher J., additional, Sørensen, Lasse Kragh, additional, Truhlar, Donald G., additional, Ugandi, Mihkel, additional, Ungur, Liviu, additional, Valentini, Alessio, additional, Vancoillie, Steven, additional, Veryazov, Valera, additional, Weser, Oskar, additional, Wesołowski, Tomasz A., additional, Widmark, Per-Olof, additional, Wouters, Sebastian, additional, Zech, Alexander, additional, Zobel, J. Patrick, additional, and Lindh, Roland, additional

Published
2019
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24. Applications to metal K pre-edges of transitionmetal dimers illustrate the approximate origin independence for the intensities in the length representation

Author

Sørensen, Lasse Kragh, Guo, Meiyuan, Lindh, Roland, Lundberg, Marcus, Sørensen, Lasse Kragh, Guo, Meiyuan, Lindh, Roland, and Lundberg, Marcus

Abstract

X-ray absorption spectroscopy (XAS) in the metal K pre-edge is a standard probe of electronic and geometric structure of transition metal complexes. Simulating the K pre-edge spectra requires contributions beyond the electric dipole, but if that term is non-zero, the second-order terms, e. g. electric quadrupoles, are no longer origin-independent. In the velocity representation, complete origin independence can be achieved by including all terms to the same order in the oscillator strength. Here, we implement that approach in the length representation and use it for restricted active space (RAS) simulations of metal K pre-edges of iron monomers and dimers. Complete origin independence is not achieved and the size of the remaining errors depends on the electric dipole oscillator strength and its ratio in length and velocity representations. The error in the origin independence is in the ANO basis sets two orders of magnitude smaller than the value of the individual contributions. For systemswith strong electric dipole contributions, the errors are not significant within 3 angstrom from a metal centre, far enough to handlemany multi-metal systems. Furthermore, we discuss the convergence of the multipole expansion, the possibility to assign spectral contributions, and the origin of negative absorption intensities. [GRAPHICS]

Published
2017
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25. Collecting all intermediates with an optimal scaling for the generalised-active-space coupled-cluster method with application to SbH

Author

Sørensen, Lasse Kragh, Olsen, Jeppe, Sørensen, Lasse Kragh, and Olsen, Jeppe

Abstract

A string-based coupled-cluster method of general excitation rank, with optimal scaling and easy collection of all possible intermediates, which accounts for special relativity within the four-component framework is presented. The easy identification and collection of intermediates is achieved by extending the excitation-class formalism and introducing a contraction order for the operator indices. Initially, all possible contractions between the Hamiltonian and the intermediateswith the cluster operator are found, stored and used for driving the algorithm, thereby defining an algorithm which allows for very complex state-selective, multi-reference, coupled-cluster calculations. The algorithm for solving the coupled-cluster equations can be used in both relativistic as well as non-relativistic calculations by appropriate restrictions in the excitation-class formalism. The capabilities of the new method are demonstrated in the application to the electronic ground state of the SbH molecule. In these calculations simulated multi-reference expansions with double, triple and quadruple excitations into the external space as well as the regular coupled-cluster hierarchy up to full quadruples excitations are compared. [GRAPHICS]

Published
2017
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26. Correlation effects in strong-field ionization of heteronuclear diatomic molecules

Author

Larsson, H. R., Bauch, S., Sørensen, Lasse Kragh, Bonitz, M., Larsson, H. R., Bauch, S., Sørensen, Lasse Kragh, and Bonitz, M.

Abstract

We develop a time-dependent theory to investigate electron dynamics and photoionization processes of diatomic molecules interacting with strong laser fields including electron-electron correlation effects. We combine the recently formulated time-dependent generalized-active-space configuration interaction theory [D. Hochstuhl and M. Bonitz, Phys. Rev. A 86, 053424 (2012); S. Bauch et al., ibid. 90, 062508 (2014)] with a prolate spheroidal basis set including localized orbitals and continuum states to describe the bound electrons and the outgoing photoelectron. As an example, we study the strong-field ionization of the two-center four-electron lithium hydride molecule in different intensity regimes. By using single-cycle pulses, two orientations of the asymmetric heteronuclear molecule are investigated: Li-H, with the electrical field pointing from H to Li, and the opposite case of H-Li. The preferred orientation for ionization is determined and we find a transition from H-Li, for low intensity, to Li-H, for high intensity. The influence of electron correlations is studied at different levels of approximation, and we find a significant change in the preferred orientation. For certain intensity regimes, even an interchange of the preferred configuration is observed, relative to the uncorrelated simulations. Further insight is provided by detailed comparisons of photoelectron angular distributions with and without correlation effects taken into account.

Published
2016
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27. Molecular orbital simulations of metal 1s2p resonant inelastic X-ray scattering

Author

Guo, Meiyuan, Erik, Källman, Sørensen, Lasse Kragh, Delcey, Mickaël G., Pinjari, Rahul V., Lundberg, Marcus, Guo, Meiyuan, Erik, Källman, Sørensen, Lasse Kragh, Delcey, Mickaël G., Pinjari, Rahul V., and Lundberg, Marcus

Abstract

For first-row transition metals, high-resolution 3d electronic structure information can be obtained using resonant inelastic X-ray scattering (RIXS). In the hard X-ray region, a K pre-edge (1s -> 3d) excitation can be followed by monitoring the dipole-allowed K alpha (2p -> 1s) or K beta (3p -> 1s) emission, processes labeled 1s2p or 1s3p RIXS. Here the restricted active space (RAS) approach, which is a molecular orbital method, is used for the first time to study hard X-ray RIXS processes. This is achieved by including the two sets of core orbitals in different partitions of the active space. Transition intensities are calculated using both first- and second-order expansions of the wave vector, including, but not limited to, electric dipoles and quadrupoles. The accuracy of the approach is tested for 1s2p RIXS of iron hexacyanides [Fe(CN)(6)](n-) in ferrous and ferric oxidation states. RAS simulations accurately describe the multiplet structures and the role of 2p and 3d spin-orbit coupling on energies and selection rules. Compared to experiment, relative energies of the two [Fe(CN)(6)](3-) resonances deviate by 0.2 eV in both incident energy and energy transfer directions, and multiplet splittings in [Fe(CN)(6)](4-) are reproduced within 0.1 eV. These values are similar to what can be expected for valence excitations. The development opens the modeling of hard X-ray scattering processes for both solution catalysts and enzymatic systems.

Published
2016
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31. Applications to metal K pre-edges of transition metal dimers illustrate the approximate origin independence for the intensities in the length representation.

Author

Sørensen, Lasse Kragh, Guo, Meiyuan, Lindh, Roland, and Lundberg, Marcus

Subjects
*TRANSITION metals, *DIMERS, *X-ray spectroscopy, *OSCILLATOR strengths, *QUADRUPOLES
Abstract

X-ray absorption spectroscopy (XAS) in the metal K pre-edge is a standard probe of electronic and geometric structure of transition metal complexes. Simulating the K pre-edge spectra requires contributions beyond the electric dipole, but if that term is non-zero, the second-order terms, e.g. electric quadrupoles, are no longer origin-independent. In the velocity representation, complete origin independence can be achieved by including all terms to the same order in the oscillator strength. Here, we implement that approach in the length representation and use it for restricted active space (RAS) simulations of metal K pre-edges of iron monomers and dimers. Complete origin independence is not achieved and the size of the remaining errors depends on the electric dipole oscillator strength and its ratio in length and velocity representations. The error in the origin independence is in the ANO basis sets two orders of magnitude smaller than the value of the individual contributions. For systems with strong electric dipole contributions, the errors are not significant within 3 Å from a metal centre, far enough to handle many multi-metal systems. Furthermore, we discuss the convergence of the multipole expansion, the possibility to assign spectral contributions, and the origin of negative absorption intensities. [ABSTRACT FROM AUTHOR]

Published
2017
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34. Setting the stage for theoretical x-ray spectra of the H 2 S molecule with multi-configurational quantum chemical calculations of the energy landscape.

Author

Ertan E, Lundberg M, Sørensen LK, and Odelius M

Abstract

In the H 2 S molecule, the interplay between different core levels can be investigated in great detail in relation to x-ray spectroscopy, which requires a theory for interpretation. Hence, valence and core excitations into the two antibonding molecular orbitals of the H 2 S molecule have been calculated within a multi-configurational wave function framework. Scanning along the S-H stretching coordinates, we derive potential energy surfaces and transition dipole moments involving the ground state and core and valence excited states. Both valence excitations and the S1s -1 and S2p -1 core excitations show pairs of dissociative and bound electronic states. These pairs of states are nearly degenerate in H 2 S at the ground state geometry. The close degeneracy together with conical intersections makes H 2 S an interesting target for x-ray spectroscopy involving ultra-fast dissociation influenced by non-adiabatic transitions and interference. For future investigations with x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), it is valuable to compare H 2 S with the water molecule, which exhibits state-selective gating to different vibrational modes [R. C. Couto et al., Nat. Commun. 8, 14165 (2017)] in its well-separated O1s -1 core excited states. The dense manifolds of the S2p -1 core excited states will complicate the analysis of K α edge RIXS, but dynamical effects could be evaluated through detuning and by comparing with L edge XAS. In L edge RIXS, the dynamical effects will be more pronounced due to the longer lifetime of the S2p -1 core excited states compared to the S1s -1 core excited states.

Published
2020
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