Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies
Abstract
Chemists are mainly interested in energy differences. In contrast, most quantum chemical methods yield the total energy which is a large number compared to the difference and has therefore to be computed to a higher relative precision than would be necessary for the difference alone. Hence, it is desirable to compute energy differences directly, thereby avoiding the precision problem. Whenever it is possible to find a parameter which transforms smoothly from an initial to a final state, the energy difference can be obtained by integrating the energy derivative with respect to that parameter (c.f., thermodynamic integration or adiabatic connection methods). If the dependence on the parameter is predominantly linear, accurate results can be obtained by singlepoint integration. In density functional theory (DFT) and HartreeFock, we applied the formalism to ionization potentials, excitation energies, and chemical bond breaking. Example calculations for ionization potentials and excitation energies showed that accurate results could be obtained with a linear estimate. For breaking bonds, we introduce a nongeometrical parameter which gradually turns the interaction between two fragments of a molecule on. The interaction changes the potentials used to determine the orbitals as well as constraining the orbitals to be orthogonal.
 Authors:
 ORNL
 Publication Date:
 Research Org.:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Center for Computational Sciences
 Sponsoring Org.:
 USDOE Office of Science (SC)
 OSTI Identifier:
 978169
 DOE Contract Number:
 DEAC0500OR22725
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Chemical Physics; Journal Volume: 125
 Country of Publication:
 United States
 Language:
 English
 Subject:
 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACCURACY; CHEMICAL BONDS; EXCITATION; FUNCTIONALS; IONIZATION POTENTIAL; THERMODYNAMICS
Citation Formats
Beste, Ariana, Harrison, Robert J, and Yanai, Takeshi. Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies. United States: N. p., 2006.
Web. doi:10.1063/1.2244559.
Beste, Ariana, Harrison, Robert J, & Yanai, Takeshi. Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies. United States. doi:10.1063/1.2244559.
Beste, Ariana, Harrison, Robert J, and Yanai, Takeshi. Sun .
"Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies". United States.
doi:10.1063/1.2244559.
@article{osti_978169,
title = {Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies},
author = {Beste, Ariana and Harrison, Robert J and Yanai, Takeshi},
abstractNote = {Chemists are mainly interested in energy differences. In contrast, most quantum chemical methods yield the total energy which is a large number compared to the difference and has therefore to be computed to a higher relative precision than would be necessary for the difference alone. Hence, it is desirable to compute energy differences directly, thereby avoiding the precision problem. Whenever it is possible to find a parameter which transforms smoothly from an initial to a final state, the energy difference can be obtained by integrating the energy derivative with respect to that parameter (c.f., thermodynamic integration or adiabatic connection methods). If the dependence on the parameter is predominantly linear, accurate results can be obtained by singlepoint integration. In density functional theory (DFT) and HartreeFock, we applied the formalism to ionization potentials, excitation energies, and chemical bond breaking. Example calculations for ionization potentials and excitation energies showed that accurate results could be obtained with a linear estimate. For breaking bonds, we introduce a nongeometrical parameter which gradually turns the interaction between two fragments of a molecule on. The interaction changes the potentials used to determine the orbitals as well as constraining the orbitals to be orthogonal.},
doi = {10.1063/1.2244559},
journal = {Journal of Chemical Physics},
number = ,
volume = 125,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

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