The Experts below are selected from a list of 164013 Experts worldwide ranked by ideXlab platform
Tom Ziegler - One of the best experts on this subject based on the ideXlab platform.
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an implementation of the conductor like screening model of solvation within the amsterdam density Functional package part ii cosmo for real solvents
Canadian Journal of Chemistry, 2009Co-Authors: Tom Ziegler, Erik Van Lenthe, Jaap Louwenj N N LouwenAbstract:The conductor-like screening model for real solvents (COSMO-RS) has been implemented in the Amsterdam density Functional Program. The surface building routines now allow for finer discretization of the GEPOL-based surfaces, and an additional surface due to Delley has been incorporated. One problem identified is the need for accurate density fitting in the region of the surface points. Another difficulty is the need to explicitly state for which atoms the hydrogen-bonding term applies. We present some vapour–liquid equilibrium curves of binary solvent systems to demonstrate the utility of the method.
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bond multiplicity in transition metal complexes applications of two electron valence indices
Journal of Physical Chemistry A, 2008Co-Authors: Artur Michalak, Roger L Dekock, Tom ZieglerAbstract:In the present study the applicability of the bond multiplicities from the Nalewajski and Mrozek valence indices was demonstrated for a variety of transition metal-based systems. The Nalewajski−Mrozek valence indices and bond multiplicity indices have been implemented in the Amsterdam Density Functional Program. Selected examples comprise the carbonyl complexes (selected tetra- and hexacarbonyls, binary monocarbonyls of the first-row transition metals), phosphines, the ligands’ trans-influence, as well as multiple metal−ligand and metal−metal bonds. The results show that the calculated bond multiplicity indices correspond well to experimental predictions based on bond lengths and vibrational frequencies for all discussed classes of complexes. Almost perfect linear correlation between the bond indices and vibrational frequencies was observed for carbonyls and the oxo complexes; the calculated bond multiplicity reproduces the accepted order for the trans-influence of different ligands, rationalizes unusuall...
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the calculation of excitation energies based on the relativistic two component zeroth order regular approximation and time dependent density Functional with full use of symmetry
Journal of Chemical Physics, 2005Co-Authors: Fan Wang, Tom Ziegler, Erik Van Lenthe, Stan J A Van Gisbergen, Evert Jan BaerendsAbstract:In the present work, we propose a relativistic time-dependent density-Functional theory (TDDFT) based on the two-component zeroth-order regular approximation and a noncollinear exchange-correlation (XC) Functional. This two-component TDDFT formalism has the correct nonrelativistic limit and affords the correct threefold degeneracy of triplet excitations. The relativistic TDDFT formalism is implemented into the AMSTERDAM DENSITY Functional Program package for closed-shell systems with full use of double-group symmetry to reduce the computational effort and facilitate the assignments. The performance of the formalism is tested on some closed-shell atoms, ions, and a few diatomic molecules containing heavy elements. The results show that the fine structure of the excited states for most atoms and ions studied here can be accurately accounted for with a proper XC potential. For the excitation energies of the molecules studied here, the present formalism shows promise and the error encountered is comparable to that of nonrelativistic TDDFT calculations on light elements.
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nuclear spin spin coupling constants from regular approximate relativistic density Functional calculations i formalism and scalar relativistic results for heavy metal compounds
Journal of Chemical Physics, 2000Co-Authors: Jochen Autschbach, Tom ZieglerAbstract:We present a relativistic formulation of the spin–spin coupling hyperfine terms based on the two component zeroth-order regular approximate Hamiltonian. The scalar relativistic parts of the resulting operators were used for an implementation into the Amsterdam density Functional Program. Application of the code for the calculation of one-bond metal-ligand couplings of systems containing 183W, 195Pt, 199Hg, and 207Pb shows that scalar relativistic calculations are able to reproduce major parts of the relativistic effects on the coupling constants, which can be even larger in magnitude than the respective total nonrelativistic values. The spatial origin of the regular approximate relativistic analogue of the Fermi-contact contribution, which is usually responsible for the strong relativistic increase of the couplings, is analyzed. Its relativistic effects can be described by the relativistic increase of valence orbital density in the very vicinity of the heavy nucleus.
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an implementation of the conductor like screening model of solvation within the amsterdam density Functional package
Theoretical Chemistry Accounts, 1999Co-Authors: Cory C Pye, Tom ZieglerAbstract:The conductor-like screening model (COSMO) of solvation has been implemented in the Amsterdam density Functional Program with maximum flexibility in mind. Four cavity definitions have been incorporated. Several iterative schemes have been tested for solving the COSMO equations. The biconjugate gradient method proves to be both robust and memory-conserving. The interaction between the surface charges and the electron density may be calculated by integrating over either the fitted or exact density, or by calculating the molecular potential. A disk-smearing algorithm is applied in the former case to avoid singularities. Several self-consistent field/COSMO coupling schemes were examined in an attempt to reduce computational effort. A gradient-preserving algorithm for removing outlying charge has been implemented. Preliminary optimized radii are given. Applications to the benzene oxide-oxepin valence tautomerization and to glycine conformation are presented.
Lucas Visscher - One of the best experts on this subject based on the ideXlab platform.
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the becke fuzzy cells integration scheme in the amsterdam density Functional Program suite
Journal of Computational Chemistry, 2013Co-Authors: Mirko Franchini, P H T Philipsen, Lucas VisscherAbstract:In this article, we document a new implementation of the fuzzy cells scheme for numerical integration in polyatomic systems [Becke, J. Chem. Phys. 1998, 88, 2547] and compare its efficiency and accuracy with respect to an integration scheme based on the Voronoi space partitioning. We show that the accuracy of both methods is comparable, but that the fuzzy cells scheme is better suited for geometry optimization. For this method, we also introduce the locally dense grid concept and present a proof-of-concept application. © 2013 Wiley Periodicals, Inc.
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performance of kinetic energy Functionals for interaction energies in a subsystem formulation of density Functional theory
Journal of Chemical Theory and Computation, 2009Co-Authors: Andreas W Gotz, S Beyan, S Maya, Lucas VisscherAbstract:We have tested the performance of a large set of kinetic energy density Functionals of the local density approximation (LDA), the gradient expansion approximation (GEA), and the generalized gradient approximation (GGA) for the calculation of interaction energies within a subsystem approach to density Functional theory. Our results have been obtained with a new implementation of interaction energies for frozen-density embedding into the Amsterdam Density Functional Program. We present data for a representative sample of 39 intermolecular complexes and 15 transition metal coordination compounds with interaction energies spanning the range from -1 to -783 kcal/mol. This is the first time that kinetic energy Functionals have been tested for such strong interaction energies as the ligand-metal bonds in the investigated coordination compounds. We confirm earlier work that GGA Functionals offer an improvement over the LDA and are particularly well suited for weak interactions like hydrogen bonds. We do, however, not find a particular reason to prefer any of the GGA Functionals over another. Functionals derived from the GEA in general perform worse for all of the weaker interactions and cannot be recommended. An unexpectedly good performance is found for the coordination compounds, in particular with the GEA-derived Functionals. However, the presently available kinetic energy Functionals cannot be applied in cases in which a density redistribution between the subsystems leads to strongly overlapping subsystem electron densities.
Evert Jan Baerends - One of the best experts on this subject based on the ideXlab platform.
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the calculation of excitation energies based on the relativistic two component zeroth order regular approximation and time dependent density Functional with full use of symmetry
Journal of Chemical Physics, 2005Co-Authors: Fan Wang, Tom Ziegler, Erik Van Lenthe, Stan J A Van Gisbergen, Evert Jan BaerendsAbstract:In the present work, we propose a relativistic time-dependent density-Functional theory (TDDFT) based on the two-component zeroth-order regular approximation and a noncollinear exchange-correlation (XC) Functional. This two-component TDDFT formalism has the correct nonrelativistic limit and affords the correct threefold degeneracy of triplet excitations. The relativistic TDDFT formalism is implemented into the AMSTERDAM DENSITY Functional Program package for closed-shell systems with full use of double-group symmetry to reduce the computational effort and facilitate the assignments. The performance of the formalism is tested on some closed-shell atoms, ions, and a few diatomic molecules containing heavy elements. The results show that the fine structure of the excited states for most atoms and ions studied here can be accurately accounted for with a proper XC potential. For the excitation energies of the molecules studied here, the present formalism shows promise and the error encountered is comparable to that of nonrelativistic TDDFT calculations on light elements.
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relativistic calculations on the adsorption of co on the 111 surfaces of ni pd and pt within the zeroth order regular approximation
Physical Review B, 1997Co-Authors: P H T Philipsen, E Van Lenthe, J G Snijders, Evert Jan BaerendsAbstract:In this paper we first describe the implementation of the zeroth-order regular approximation ~ZORA! for relativistic effects in our density-Functional Program for extended systems. The ZORA formalism affords approximations, which are discussed and tested, that reduce the computational effort of scalar relativistic calculations to that of nonrelativistic calculations, the inclusion of spin-orbit coupling requiring additional effort. Second, we present the outcome of nonrelativistic, scalar relativistic, and spin-orbit coupling calculations on the adsorption energy of CO on the ~111! surfaces of Ni, Pd, and Pt. Relativity has a modest effect for CO on Pd, but proves to be essential for CO on Pt. The relativistic correction for the CO/Pt adsorption energy is as large as 70% at the scalar relativistic level and 55% when including spin-orbit coupling. In addition, relativity changes the preferred adsorption site for CO/Pt from hollow to top. We have examined the effects of spin polarization and of different exchange-correlation Functionals, i.e., the local-density approximation ~LDA! versus two generalized gradient approximations ~GGA!. The GGA’s correct the severe overbinding by LDA of CO to the metal surfaces, and yield good agreement with experiment for adsorption energies and sites. @S0163-1829~97!04740-1#
Yulia Korukhova - One of the best experts on this subject based on the ideXlab platform.
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An approach to automatic deductive synthesis of Functional Programs
Annals of Mathematics and Artificial Intelligence, 2007Co-Authors: Yulia KorukhovaAbstract:The work deals with automatic deductive synthesis of Functional Programs. Formal specification of a Program is taken as a mathematical existence theorem and while proving it, we derive a Program and simultaneously prove that this Program corresponds to given specification. Several problems have to be resolved for automatic synthesis: the choice of synthesis rules that allows us to derive the basic constructions of a Functional Program, order of rule application and choice of a particular induction rule. The method proposed here is based on the deductive tableau method. The basic method gives rules for Functional Program construction. To determine the proof strategy we use some external heuristics, including rippling. And for the induction hypothesis formation the combination of rippling and the deductive tableau method became very useful. The proposed techniques are implemented in the system ALISA (Automatic Lisp Synthesizer) and used for automatic synthesis of several functions in the Lisp language.
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automatic deductive synthesis of lisp Programs in the system alisa
Lecture Notes in Computer Science, 2006Co-Authors: Yulia KorukhovaAbstract:The work deals with deductive synthesis of Functional Programs. During this synthesis formal specification of a Program is taken as a mathematical existence theorem and while proving it, we derive a Program and prove that this Program corresponds to given specification. Our method of synthesis is based on the deductive tableau method, that allows to derive three basic constructions of a Functional Program. But the full search of possible proof attempts in the deductive tableau induces a very large search space; the proof is needed to be guided. For using this method in the automatic mode additional heuristics are required. Some of such heuristics are proposed in this work. They consist in proof planning by using rippling and in the use of sorted logic with type hierarchy that reduces search space and blocks some branches of proof, corresponding to synthesis of incorrect functions. The proposed techniques are implemented in the system ALISA 1 and used for automatic synthesis of several functions on Lisp language.
Scott Owens - One of the best experts on this subject based on the ideXlab platform.
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proof producing translation of higher order logic into pure and stateful ml
Journal of Functional Programming, 2014Co-Authors: Magnus O Myreen, Scott OwensAbstract:The higher-order logic found in proof assistants such as Coq and various HOL systems provides a convenient setting for the development and verification of Functional Programs. However, to efficiently run these Programs, they must be converted (or ‘extracted’) to Functional Programs in a Programming language such as ML or Haskell. With current techniques, this step, which must be trusted, relates similar looking objects that have very different semantic definitions, such as the set-theoretic model of a logic and the operational semantics of a Programming language. In this paper, we show how to increase the trustworthiness of this step with an automated technique. Given a Functional Program expressed in higher-order logic, our technique provides the corresponding Program for a Functional language defined with an operational semantics, and it provides a mechanically checked theorem relating the two. This theorem can then be used to transfer verified properties of the logical function to the Program. We have implemented our technique in the HOL4 theorem prover, translating functions to a subset of Standard ML, and have applied the implementation to examples including Functional data structures, a parser generator, cryptographic algorithms, a garbage collector and the 500-line kernel of the HOL light theorem prover. This paper extends our previous conference publication with new material that shows how functions defined in terms of a state-and-exception monad can be translated, with proofs, into stateful ML code. The HOL light example is also new.
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proof producing synthesis of ml from higher order logic
International Conference on Functional Programming, 2012Co-Authors: Magnus O Myreen, Scott OwensAbstract:The higher-order logic found in proof assistants such as Coq and various HOL systems provides a convenient setting for the development and verification of pure Functional Programs. However, to efficiently run these Programs, they must be converted (or "extracted") to Functional Programs in a Programming language such as ML or Haskell. With current techniques, this step, which must be trusted, relates similar looking objects that have very different semantic definitions, such as the set-theoretic model of a logic and the operational semantics of a Programming language. In this paper, we show how to increase the trustworthiness of this step with an automated technique. Given a Functional Program expressed in higher-order logic, our technique provides the corresponding Program for a Functional language defined with an operational semantics, and it provides a mechanically checked theorem relating the two. This theorem can then be used to transfer verified properties of the logical function to the Program. We have implemented our technique in the HOL4 theorem prover, translating functions to a core subset of Standard ML, and have applied it to examples including Functional data structures, a parser generator, cryptographic algorithms, and a garbage collector.
