Quim Chaves - Academia.edu (original) (raw)
Papers by Quim Chaves
Journal of Computational Chemistry, 2005
This article reports the numerical comparison of the quantities characterizing the extent of elec... more This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified.
Journal of Mathematical Chemistry, Nov 25, 2010
The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented y... more The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented years ago [E. Besalú and R. Carbó-Dorca, J. Math. Chem., 22, 85 (1997)] can be modified and expressed in terms of operators, opening the possibility to define diverse variants with better convergence properties. This methodology is called here modified autoadjusting perturbation theory which is superior, at least numerically, to Rayleigh Schrödinger perturbation theory and the superconvergent perturbation theory [W. Scherer, Phys. Rev. Lett., 74, 1495 (1995)] applied to the one-dimensional quartic anharmonic oscillator. The new feature of this method is the Hamiltonian modifier which can be chosen in a proper way in order to improve the calculations and to obtain convergent energy series and wavefunction when Rayleigh Schrödinger perturbation theory gives divergent ones. Resummation techniques are used to check whether the correction terms of modified autoadjusting perturbation theory series resums similarly to the Rayleigh Schrödinger perturbation one. The iterative nature of the proposed method allows for a linear time scaling and for memory economization when it is numerically implemented.
Journal of Mathematical Chemistry, 2010
The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented y... more The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented years ago [E. Besalú and R. Carbó-Dorca, J. Math. Chem., 22, 85 (1997)] can be modified and expressed in terms of operators, opening the possibility to define diverse variants with better convergence properties. This methodology is called here modified autoadjusting perturbation theory which is superior, at least numerically, to Rayleigh Schrödinger perturbation theory and the superconvergent perturbation theory [W. Scherer, Phys. Rev. Lett., 74, 1495 (1995)] applied to the one-dimensional quartic anharmonic oscillator. The new feature of this method is the Hamiltonian modifier which can be chosen in a proper way in order to improve the calculations and to obtain convergent energy series and wavefunction when Rayleigh Schrödinger perturbation theory gives divergent ones. Resummation techniques are used to check whether the correction terms of modified autoadjusting perturbation theory series resums similarly to the Rayleigh Schrödinger perturbation one. The iterative nature of the proposed method allows for a linear time scaling and for memory economization when it is numerically implemented.
Journal of Computational Chemistry, 2005
This article reports the numerical comparison of the quantities characterizing the extent of elec... more This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified.
Journal of Computational Chemistry, 2006
This article reports the application of a recently proposed formalism of domain averaged Fermi ho... more This article reports the application of a recently proposed formalism of domain averaged Fermi holes to the problem of the localization of electron pairs in electron localization function (ELF) domains and its possible implications for the electron pair model of chemical bond. The main focus was on the systems, such as H 2 O or N 2 , in which the ''unphysical'' population of ELF domains makes the parallel between these domains and chemical bond questionable. On the basis of the results of the Fermi-hole analysis, we propose that the above problems could be due to the fact that in some cases the boundaries of the ELF domains need not be determined precisely enough.
Ecosystems, 2009
Ó 2009 Springer Science+Business Media, LLC 961 pasture agriculture in the tropics shifts toward ... more Ó 2009 Springer Science+Business Media, LLC 961 pasture agriculture in the tropics shifts toward intensive crop cultivation.
Journal of Computational Chemistry, 2005
This article reports the numerical comparison of the quantities characterizing the extent of elec... more This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified.
Journal of Mathematical Chemistry, Nov 25, 2010
The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented y... more The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented years ago [E. Besalú and R. Carbó-Dorca, J. Math. Chem., 22, 85 (1997)] can be modified and expressed in terms of operators, opening the possibility to define diverse variants with better convergence properties. This methodology is called here modified autoadjusting perturbation theory which is superior, at least numerically, to Rayleigh Schrödinger perturbation theory and the superconvergent perturbation theory [W. Scherer, Phys. Rev. Lett., 74, 1495 (1995)] applied to the one-dimensional quartic anharmonic oscillator. The new feature of this method is the Hamiltonian modifier which can be chosen in a proper way in order to improve the calculations and to obtain convergent energy series and wavefunction when Rayleigh Schrödinger perturbation theory gives divergent ones. Resummation techniques are used to check whether the correction terms of modified autoadjusting perturbation theory series resums similarly to the Rayleigh Schrödinger perturbation one. The iterative nature of the proposed method allows for a linear time scaling and for memory economization when it is numerically implemented.
Journal of Mathematical Chemistry, 2010
The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented y... more The aim of this paper is to show that the so-called Autoadjusting Perturbation Theory presented years ago [E. Besalú and R. Carbó-Dorca, J. Math. Chem., 22, 85 (1997)] can be modified and expressed in terms of operators, opening the possibility to define diverse variants with better convergence properties. This methodology is called here modified autoadjusting perturbation theory which is superior, at least numerically, to Rayleigh Schrödinger perturbation theory and the superconvergent perturbation theory [W. Scherer, Phys. Rev. Lett., 74, 1495 (1995)] applied to the one-dimensional quartic anharmonic oscillator. The new feature of this method is the Hamiltonian modifier which can be chosen in a proper way in order to improve the calculations and to obtain convergent energy series and wavefunction when Rayleigh Schrödinger perturbation theory gives divergent ones. Resummation techniques are used to check whether the correction terms of modified autoadjusting perturbation theory series resums similarly to the Rayleigh Schrödinger perturbation one. The iterative nature of the proposed method allows for a linear time scaling and for memory economization when it is numerically implemented.
Journal of Computational Chemistry, 2005
This article reports the numerical comparison of the quantities characterizing the extent of elec... more This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified.
Journal of Computational Chemistry, 2006
This article reports the application of a recently proposed formalism of domain averaged Fermi ho... more This article reports the application of a recently proposed formalism of domain averaged Fermi holes to the problem of the localization of electron pairs in electron localization function (ELF) domains and its possible implications for the electron pair model of chemical bond. The main focus was on the systems, such as H 2 O or N 2 , in which the ''unphysical'' population of ELF domains makes the parallel between these domains and chemical bond questionable. On the basis of the results of the Fermi-hole analysis, we propose that the above problems could be due to the fact that in some cases the boundaries of the ELF domains need not be determined precisely enough.
Ecosystems, 2009
Ó 2009 Springer Science+Business Media, LLC 961 pasture agriculture in the tropics shifts toward ... more Ó 2009 Springer Science+Business Media, LLC 961 pasture agriculture in the tropics shifts toward intensive crop cultivation.