Item


Describing dissociation in variational second order density matrix theory

A correct description of dissociating bonds is even more challenging to methods based on the density or first or second order density matrices than to wave function based techniques. Density and density matrix based techniques typically yield dissociated states with fractional charges instead of correct integer charges. Such non-physical fractionally charged dissociated states also occur in variational second order density matrix theory[1] under the necessary but not sufficient P-, Q- and G-condition for Nrepresentability. Additional N-representability constraints are needed to correct them. To this end, we introduced linear constraints on the energy of atomic subspaces in the molecule. This work focuses on the implementation of such subspace constraints, more specifically on the identification of the tightest set of subspace constraints, their scale-up to bigger molecules and their relationship to size-consistency. These issues are discussed in relation to the potential energy surface of the F3 - ion. First of all, the subspace constraints enforce size-consistency and a correct dissociation, but do not improve the accuracy of the method at short bond lengths, where they are not active. They only become active when one or more bonds are stretched. Furthermore, while only a small number of subspace constraints suffices to obtain the correct dissociation, the constraints are geometry dependent. They are therefore quite laborious to apply to large potential energy surfaces

Universitat de Girona. Departament de Química

Universitat de Girona. Institut de Química Computacional

Author: Van Aggelen, Helen
Date: 2010 July 8
Abstract: A correct description of dissociating bonds is even more challenging to methods based on the density or first or second order density matrices than to wave function based techniques. Density and density matrix based techniques typically yield dissociated states with fractional charges instead of correct integer charges. Such non-physical fractionally charged dissociated states also occur in variational second order density matrix theory[1] under the necessary but not sufficient P-, Q- and G-condition for Nrepresentability. Additional N-representability constraints are needed to correct them. To this end, we introduced linear constraints on the energy of atomic subspaces in the molecule. This work focuses on the implementation of such subspace constraints, more specifically on the identification of the tightest set of subspace constraints, their scale-up to bigger molecules and their relationship to size-consistency. These issues are discussed in relation to the potential energy surface of the F3 - ion. First of all, the subspace constraints enforce size-consistency and a correct dissociation, but do not improve the accuracy of the method at short bond lengths, where they are not active. They only become active when one or more bonds are stretched. Furthermore, while only a small number of subspace constraints suffices to obtain the correct dissociation, the constraints are geometry dependent. They are therefore quite laborious to apply to large potential energy surfaces
Format: video/H263
audio/mpeg
Citation: Van Aggelen, H. (2010). Describing dissociation in variational second order density matrix theory. A ’IX Girona Seminar’. Girona: Universitat. [Consulta 7 setembre 2010]. Disponible a: http://hdl.handle.net/10256.1/1729
Document access: http://hdl.handle.net/10256.1/1729
Language: eng
Publisher: Universitat de Girona. Departament de Química
Universitat de Girona. Institut de Química Computacional
Collection: IX Girona Seminar
Rights: Aquest document està subjecte a una llicència Creative Commons: Reconeixement - No comercial - Compartir igual (by-nc-sa)
Rights URI: http://creativecommons.org/licenses/by-nc-sa/3.0/es/deed.ca
Subject: Química quàntica -- Congressos
Quantum chemistry -- Congresses
Title: Describing dissociation in variational second order density matrix theory
Type: info:eu-repo/semantics/lecture
Repository: DUGiMedia

Subjects

Authors