Electron correlation by polarization of interacting densities

Whitten, J. L.

doi:10.1063/1.4975329

Cited by 4 publications

(2 citation statements)

References 15 publications

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“…Each molecule is described by a double zeta basis of near Hartree-Fock atomic orbitals, contracted as 1s, 2s, and 2p orbitals plus additional two-term functions formed by taking the two longest exponent components of the 2s and 2p orbitals as a separate basis functions, dfunctions are included in one system. 21 In the present study, all atoms with the same atomic number in the same molecule have the same potential (density) and no distinction is made between atoms in different bonding environments. Thus, the present results are an upper bound on the energy that would be improved if densities for an atom were allowed to vary within the molecule.…”

Section: Application To Single-determinant Scf Wavefunctions and Conf...mentioning

confidence: 96%

Prediction of many-electron wavefunctions using atomic potentials

Nazari

Whitten

2017

The Journal of Chemical Physics

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For a given many-electron molecule, it is possible to define a corresponding one-electron Schrödinger equation, using potentials derived from simple atomic densities, whose solution predicts fairly accurate molecular orbitals for single- and multi-determinant wavefunctions for the molecule. The energy is not predicted and must be evaluated by calculating Coulomb and exchange interactions over the predicted orbitals. Potentials are found by minimizing the energy of predicted wavefunctions. There exist slightly less accurate average potentials for first-row atoms that can be used without modification in different molecules. For a test set of molecules representing different bonding environments, these average potentials give wavefunctions with energies that deviate from exact self-consistent field or configuration interaction energies by less than 0.08 eV and 0.03 eV per bond or valence electron pair, respectively.

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Section: Application To Single-determinant Scf Wavefunctions and Conf...mentioning

confidence: 96%

Prediction of many-electron wavefunctions using atomic potentials

Nazari

Whitten

2017

The Journal of Chemical Physics

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“…The method has been recently extended to Ti, Fe, and Ni, as well as functional group specific potentials. 83 However, as it is well-known that orbital optimization in HF and DFT can be reformulated as a problem of finding the right optimized effective potential, 84 it is difficult to estimate how well and how easily the results of refs (82) and 83 can be generalized to the rest of the periodic table, or even how the method generalizes beyond the nonstandard 85 “‘double-ζ”’ and “‘triple-ζ”’ basis sets of ‘‘near Hartree–Fock atomic orbitals’’ used in the study.…”

Section: Theorymentioning

confidence: 99%

Assessment of Initial Guesses for Self-Consistent Field Calculations. Superposition of Atomic Potentials: Simple yet Efficient

Lehtola

2019

J. Chem. Theory Comput.

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Electronic structure calculations, such as in the Hartree–Fock or Kohn–Sham density functional approach, require an initial guess for the molecular orbitals. The quality of the initial guess has a significant impact on the speed of convergence of the self-consistent field (SCF) procedure. Popular choices for the initial guess include the one-electron guess from the core Hamiltonian, the extended Hückel method, and the superposition of atomic densities (SAD). Here, we discuss alternative guesses obtained from the superposition of atomic potentials (SAP), which is easily implementable even in real-space calculations. We also discuss a variant of SAD which produces guess orbitals by purification of the density matrix that could also be used in real-space calculations, as well as a parameter-free variant of the extended Hückel method, which resembles the SAP method and is easy to implement on top of existing SAD infrastructure. The performance of the core Hamiltonian, the SAD, and the SAP guesses as well as the extended Hückel variant is assessed in nonrelativistic calculations on a data set of 259 molecules ranging from the first to the fourth periods by projecting the guess orbitals onto precomputed, converged SCF solutions in single- to triple-ζ basis sets. It is shown that the proposed SAP guess is the best guess on average. The extended Hückel guess offers a good alternative, with less scatter in accuracy.

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Estimates of electron correlation based on density expansions

Whitten

2020

The Journal of Chemical Physics

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Methods for estimating the correlation energy of molecules and other electronic systems are discussed based on the assumption that the correlation energy can be partitioned between atomic regions. In one method, the electron density is expanded in terms of atomic contributions using rigorous electron repulsion bounds, and, in a second method, correlation contributions are associated with basis function pairs. The methods do not consider the detailed nature of localized excitations, but instead define a correlation energy per electron factor that that is unique to a specific atom. The correlation factors are basis function dependent and are determined by from configuration interaction calculations on diatomic and hydride molecules. The correlation energy estimates are compared with the results of high-level configuration interaction calculations for a test set of twenty-seven molecules representing a wide range of bonding environments (average error of 2.6%). An extension based on truncated CI calculations in which d-and hydrogen p-type functions are eliminated from the virtual space combined with estimates of dynamical correlation contributions using atomic correlation factors is discussed and applied to the dissociation of several molecules.

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Electron correlation by polarization of interacting densities

Cited by 4 publications

References 15 publications

Prediction of many-electron wavefunctions using atomic potentials

Prediction of many-electron wavefunctions using atomic potentials

Assessment of Initial Guesses for Self-Consistent Field Calculations. Superposition of Atomic Potentials: Simple yet Efficient

Estimates of electron correlation based on density expansions

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