| 1. |
- Brändas, Erkki, Professor Emeritus, 1940-
(author)
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It from bit : AI and the laws of nature
- 2023
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In: International Journal of Quantum Chemistry. - : John Wiley & Sons. - 0020-7608 .- 1097-461X. ; 124:1
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Journal article (peer-reviewed)abstract
- The present rate of growth of powerful AI systems motivates an accurate comparisonbetween the notion of computers and the workings of natural sciences. Statements such as “intelligence doesn't require flesh, blood or carbon atoms” or “it's computation all the way down” incite a substrate-independent view, providing shortcuts for Darwinian evolution and the possible appearance of sentient machines. This view is discussed and contrasted from a quantum chemical perspective. The qualitative difference between the developed AI and the evolved HI is recognized and the importance of a material constituent, formulated in terms of energy-temperature, conjugate to an immaterial ingredient, in the context of time-entropy, is pointed out as a necessary feature. The popular dictum “it from bit” does not appear valid unless amended with its obverse “bit from it.”
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| 2. |
- Kowalewski, Markus, 1980-, et al.
(author)
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Sustainable packaging of quantum chemistry software with the Nix package manager
- 2022
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In: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 122:9
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Journal article (peer-reviewed)abstract
- The installation of quantum chemistry software packages is commonly done manually and can be a time-consuming and complicated process. An update of the underlying Linux system requires a reinstallation in many cases and can quietly break software installed on the system. In this paper, we present an approach that allows for an easy installation of quantum chemistry software packages, which is also independent of operating system updates. The use of the Nix package manager allows building software in a reproducible manner, which allows for a reconstruction of the software for later reproduction of scientific results. The build recipes that are provided can be readily used by anyone to avoid complex installation procedures.
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| 3. |
- Laestadius, Andre, et al.
(author)
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Unique continuation for the magnetic Schrödinger equation
- 2020
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In: International Journal of Quantum Chemistry. - : WILEY. - 0020-7608 .- 1097-461X. ; 120:8
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Journal article (peer-reviewed)abstract
- The unique-continuation property from sets of positive measure is here proven for the many-body magnetic Schrodinger equation. This property guarantees that if a solution of the Schrodinger equation vanishes on a set of positive measure, then it is identically zero. We explicitly consider potentials written as sums of either one-body or two-body functions, typical for Hamiltonians in many-body quantum mechanics. As a special case, we are able to treat atomic and molecular Hamiltonians. The unique-continuation property plays an important role in density-functional theories, which underpins its relevance in quantum chemistry.
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| 4. |
- Lantz, Victor, et al.
(author)
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Deep learning for inverse problems in quantum mechanics
- 2021
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In: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 121:9
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Journal article (peer-reviewed)abstract
- Inverse problems are important in quantum mechanics and involve such questions as finding which potential give a certain spectrum or which arrangement of atoms give certain properties to a molecule or solid. Inverse problems are typically very hard to solve and tend to be very compute intense. We here show that neural networks can easily solve inverse problems in quantum mechanics. It is known that a neural network can compute the spectrum of a given potential, a result which we reproduce. We find that the (much harder) inverse problem of computing the correct potential that gives a prescribed spectrum is equally easy for a neural network. We extend previous work where neural networks were used to find the electronic many-particle density given a potential by considering the inverse problem. That is, we show that neural networks can compute the potential that gives a prescribed many-electron density.
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| 5. |
- Mukhopadhyaya, Aritra, et al.
(author)
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Probing the spin states of tetra-coordinated iron(II) porphyrins by their vibrational and pre K-edge x-ray absorption spectra
- 2023
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In: International Journal of Quantum Chemistry. - : John Wiley & Sons. - 0020-7608 .- 1097-461X. ; 123:18
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Journal article (peer-reviewed)abstract
- Tetra-coordinated iron(II) porphyrins are observed in triplet (intermediate spin, IS) ground state with low-lying quintet (high spin, HS) and singlet (low spin, LS) excited states. It is well known in the literature that the d(Fe_N) bond distances are dependent on the spin state such that the d(Fe_N) distances are larger for HS compared to the LS/IS states. This implies the existence of strong magneto-structural correlations. Herein, the possibility to obtain the spin-state information for a series of tetra-coordinated square planar iron(II) porphyrin complexes have been explored by exploiting the magneto-structural correlations obtained from first principle calculations. The spin-state dependent nature of the chemical bonds and spin polarization on the N-atoms play a crucial role in the vibrational dynamics of the central Fe-atom. Theoretical nuclear resonance vibrational spectroscopy (NRVS) is adopted to investigate the vibrational dynamics and the Fe-atom associated spectral peaks and their spin-dependent features. We find that NRVS studies along with iron pre-K-edge x-ray absorption analysis convincingly provide the information on the spin state, which could be utilized to identify the spin states without adopting any magnetic probes.
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| 6. |
- Oliveira, Joao P. C., et al.
(author)
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Linear response of the indirectJ-coupling alternation to the energy gap of increasing pi-conjugated oligomers
- 2020
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In: International Journal of Quantum Chemistry. - : WILEY. - 0020-7608 .- 1097-461X.
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Journal article (peer-reviewed)abstract
- We have investigated the dependence of the electronic energy gap of organic conjugated oligomers on theJ-coupling alternation (JCA) parameter, derived from the nuclear magnetic resonance (NMR) spectroscopy. We exploit the systematic and concerted oscillations observed for the indirect spin-spin coupling constants (SSCCs), between two adjacent(13)C nuclei ((1)J(CC)), in the pi-conjugated systems. Hence, we define a scalar JCA parameter in terms of the differences of(1)J(CC), which is further analyzed as a function of the HOMO-LUMO gaps (the energy difference between the frontier molecular orbitals), as well as other properties of the studied oligomers. Using an adequate exchange-correlation density functional approach, we show that, for all systems considered here, that is, polyacetylene (PA), poly(para-phenylene) (PPP), polypyrrole (PPy), and polythiophene (PTh), their calculated electronic energy gaps may exhibit a linear dependence on the JCA. Our results indicate that a single-valued NMR-based parameter properly renders the electronic features of highly conjugated oligomers, allowing us to compare the strengths ofJ-couplings in different systems. The present description yields a way to capture both the bonding features and the electronic absorption of these systems provided by the SSCCs. The JCA gives evidence for the differences in the electronic structure of distinct classes of conjugated systems, such as PA, and those that can exhibit a quinoid character, such as PPP, PPy, and PTh.
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| 7. |
- Sørensen, Lasse K.
(author)
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Nakatsuji's theorem of the necessary and sufficient conditions of the wave function revisited
- 2021
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In: International Journal of Quantum Chemistry. - : John Wiley and Sons Inc. - 0020-7608 .- 1097-461X. ; 121:23
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Journal article (peer-reviewed)abstract
- We will here revisit Nakatsuji's theorem of the necessary and sufficient conditions of the wave function and reinterpret these conditions in the new light of our findings. It will here be shown that the equations for the necessary and sufficient conditions are not independent and that these equations can be reduced to a single equation. This observation reduces the number of conditions for the wave function for the electronic Hamiltonian to (Formula presented.), where (Formula presented.) is the number of basis functions, which coincide with the number of parameters in the two-particle reduced density matrix. Since only the highest order electron interaction term determines the necessary and sufficient conditions Nakatsuji's theorem can in this way be interpreted as a generalized Brillouin theorem. In this way the stationary conditions for the wave function of Hamiltonians with any n-body interaction takes a similar form. It is hoped that this new interpretation of the necessary and sufficient conditions as a generalized Brillouin theorem can give insights into the development of novel and compact representations of the wave function.
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