The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
L. Wolniewicz - One of the best experts on this subject based on the ideXlab platform.
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Rotation-vibrational states of H2D+ using hyperspherical coordinates and harmonics
Molecular Physics, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:Using the highly accurate Rohse-Kutzelnigg-Jaquet-Klopper potential surface the band origins up to 9000 cm-1 have been calculated for H2D+. Ro-vibrational term values have been calculated up to J = 12 for the vibrational ground state, up to J = 8 for the singly excited states and up to J = 4 for the doubly excited states. The relation between exact hyperspherical quantum numbers and the usual spectroscopic quantum numbers is discussed and the results obtained are compared with the available experimentally observed transition energies. As many of the calculated terms have not been observed yet, the data presented should aid experimental assignments.
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Rotation-vibrational states of H3+ using hyperspherical coordinates and harmonics
Berichte der Bunsengesellschaft für physikalische Chemie, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:A new method for calculating rotation-vibrational states of triatomic molecules is presented. It is based on an expansion of the wavefunction in terms of hyperspherical harmonics, which cover five coordinates, and numerical integration of the resulting set of differential equations in the remaining coordinate, the hyperradius ρ. The method is applied to H + 3 . Here we compare the results for two electronic surfaces, the Meyer-Botschwina-Burton surface and the new surface by Kutzelnigg and coworkers
Wim Klopper - One of the best experts on this subject based on the ideXlab platform.
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werner Kutzelnigg full of ideas
Molecular Physics, 2020Co-Authors: Volker Staemmler, Wim KlopperAbstract:From the 30th of June until the 5th of July 2019, the 9th Molecular Quantum Mechanics conference (MQM 2019) took place in the ‘Kongresshaus Stadthalle’ in Heidelberg, Germany. The conference had be...
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Werner Kutzelnigg – full of ideas
Molecular Physics, 2020Co-Authors: Volker Staemmler, Wim KlopperAbstract:From the 30th of June until the 5th of July 2019, the 9th Molecular Quantum Mechanics conference (MQM 2019) took place in the ‘Kongresshaus Stadthalle’ in Heidelberg, Germany. The conference had be...
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The geminal basis in explicitly correlated wave functions
Chemical Physics, 2009Co-Authors: Sebastian Höfener, Wim Klopper, Trygve HelgakerAbstract:Abstract In 1985 Kutzelnigg showed that a large percentage of the electron correlation energy for helium can be recovered using a single explicitly correlated basis function, chosen to fit the cusp at the correlation hole. In particular the simple wave function Ψ = ( 1 + 1 2 r 12 ) Φ returned more than 80% of the correlation energy. In this paper we return to Kutzelnigg’s simple ansatz and remove the conventional double excitations in explicitly correlated CC2 theory (denoted as CCS(F12)), applying all established developments in modern F12 theory, such as replacing linear r 12 with f ( r 12 ) = exp(− γr 12 ) and the use of auxiliary basis sets for the standard RI approximation in R12 theory. Analysing different approximations we show that in general the CCS(F12) approach yields 80–95% of the CC2 correlation energy, which is astonishingly large considering the small number and restricted form of the geminal basis functions.
Alexander Alijah - One of the best experts on this subject based on the ideXlab platform.
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Rotation-vibrational states of H2D+ using hyperspherical coordinates and harmonics
Molecular Physics, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:Using the highly accurate Rohse-Kutzelnigg-Jaquet-Klopper potential surface the band origins up to 9000 cm-1 have been calculated for H2D+. Ro-vibrational term values have been calculated up to J = 12 for the vibrational ground state, up to J = 8 for the singly excited states and up to J = 4 for the doubly excited states. The relation between exact hyperspherical quantum numbers and the usual spectroscopic quantum numbers is discussed and the results obtained are compared with the available experimentally observed transition energies. As many of the calculated terms have not been observed yet, the data presented should aid experimental assignments.
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Rotation-vibrational states of H3+ using hyperspherical coordinates and harmonics
Berichte der Bunsengesellschaft für physikalische Chemie, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:A new method for calculating rotation-vibrational states of triatomic molecules is presented. It is based on an expansion of the wavefunction in terms of hyperspherical harmonics, which cover five coordinates, and numerical integration of the resulting set of differential equations in the remaining coordinate, the hyperradius ρ. The method is applied to H + 3 . Here we compare the results for two electronic surfaces, the Meyer-Botschwina-Burton surface and the new surface by Kutzelnigg and coworkers
Werner Kutzelnigg - One of the best experts on this subject based on the ideXlab platform.
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Density cumulant functional theory: First implementation and benchmark results for the DCFT-06 model
Journal of Chemical Physics, 2010Co-Authors: Andrew C. Simmonett, Jeremiah J. Wilke, Henry F. Schaefer, Werner KutzelniggAbstract:Density cumulant functional theory [W. Kutzelnigg, J. Chem. Phys. 125, 171101 (2006)] is implemented for the first time. Benchmark results are provided for atoms and diatomic molecules, demonstrating the performance of DCFT-06 for both nonbonded and bonded interactions. The results show that DCFT-06 appears to perform similarly to coupled cluster theory with single and double excitations (CCSD) in describing dispersion. For covalently bound systems, the physical properties predicted by DCFT-06 appear to be at least of CCSD quality around equilibrium geometries. The computational scaling of both DCFT-06 and CCSD is O(N6), but the former has reduced nonlinearities among the variables and a Hermitian energy functional, making it an attractive alternative.
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Relativistic theory of nuclear magnetic resonance parameters in a Gaussian basis representation
Journal of Chemical Physics, 2009Co-Authors: Werner KutzelniggAbstract:The calculation of NMR parameters from relativistic quantum theory in a Gaussian basis expansion requires some care. While in the absence of a magnetic field the expansion in a kinetically balanced basis converges for the wave function in the mean and for the energy with any desired accuracy, this is not necessarily the case for magnetic properties. The results for the magnetizability or the nuclear magnetic shielding are not even correct in the nonrelativistic limit (nrl) if one expands the original Dirac equation in a kinetically balanced Gaussian basis. This defect disappears if one starts from the unitary transformed Dirac equation as suggested by Kutzelnigg [Phys. Rev. A 67, 032109 (2003)]. However, a new difficulty can arise instead if one applies the transformation in the presence of the magnetic field of a point nucleus. If one decomposes certain contributions, the individual terms may diverge, although their sum is regular. A controlled cancellation may become difficult and numerical instabilitie...
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Irreducible Brillouin conditions and contracted Schrodinger equations for n-electron systems. II. Spin-free formulation
Journal of Chemical Physics, 2002Co-Authors: Werner Kutzelnigg, Debashis MukherjeeAbstract:Recently [W. Kutzelnigg and D. Mukherjee, Chem. Phys. Lett. 317, 567 (2000); D. Mukherjee and W. Kutzelnigg, J. Chem. Phys 114, 2047 (2001)] the irreducible k-particle Brillouin conditions IBC k and the irreducible k-particle contracted Schrodinger equations ICSE k were derived. These permit the definition of a hierarchy of k-particle approximations for the direct calculation of the cumulants λ k of the k-particle density matrices. Now, the spin-free form of these conditions, appropriate for a spin-free Hamiltonian, is given. This is particularly useful for open-shell states. The definition of the cumulants of the reduced densities has to be generalized for these anyway, making use of irreducible tensor operators with respect to SU 2 . There are two alternative definitions of spin-free cumulants, of which the one in terms of spin-free reduced density matrices appears to be preferable. Alternatively to the straight spin-free formulation, we also present a theory in terms of spin-free operators adapted to the symmetric group. Partial trace relations that relate the elements of the cumulants of different particle rank are derived. There are partial trace relations for "exchange elements," which are determined by the total spin quantum number S. From these relations the individual exchange elements of Λ 2 can be obtained in special cases. This allows a simple formulation of the stationarity conditions for open-shell states of any spin multiplicity.
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Kann man wissenschaftliche Leistung messen
Nachrichten Aus Chemie Technik Und Laboratorium, 1998Co-Authors: Werner KutzelniggAbstract:Die „Qualitat” eines Wissenschaftlers wird allzu oft noch nach der Anzahl seiner Publikationen beurteilt - ein allzu unvollkommenes Kriterium, wie Werner Kutzelnigg in diesem Beitrag beweist. Der Neugierige, der das Problem von allen Seiten beleuchtet, steht aber schnell vor einem Dilemma: „Citation-Rankings” taugen wenig, aber Kriterien mit mehr Aussagekraft sind schwer zu greifen.
Juergen Hinze - One of the best experts on this subject based on the ideXlab platform.
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Rotation-vibrational states of H2D+ using hyperspherical coordinates and harmonics
Molecular Physics, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:Using the highly accurate Rohse-Kutzelnigg-Jaquet-Klopper potential surface the band origins up to 9000 cm-1 have been calculated for H2D+. Ro-vibrational term values have been calculated up to J = 12 for the vibrational ground state, up to J = 8 for the singly excited states and up to J = 4 for the doubly excited states. The relation between exact hyperspherical quantum numbers and the usual spectroscopic quantum numbers is discussed and the results obtained are compared with the available experimentally observed transition energies. As many of the calculated terms have not been observed yet, the data presented should aid experimental assignments.
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Rotation-vibrational states of H3+ using hyperspherical coordinates and harmonics
Berichte der Bunsengesellschaft für physikalische Chemie, 1995Co-Authors: Alexander Alijah, Juergen Hinze, L. WolniewiczAbstract:A new method for calculating rotation-vibrational states of triatomic molecules is presented. It is based on an expansion of the wavefunction in terms of hyperspherical harmonics, which cover five coordinates, and numerical integration of the resulting set of differential equations in the remaining coordinate, the hyperradius ρ. The method is applied to H + 3 . Here we compare the results for two electronic surfaces, the Meyer-Botschwina-Burton surface and the new surface by Kutzelnigg and coworkers
