Spectral Theory of Physical and Chemical Binding: Aspects of Computational Implementation

Langhoff, P. W.; Boatz, Jerry A.; Sheehy, Jeffery A.

doi:10.21236/ada397877

Cited by 2 publications

(12 citation statements)

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“…Potential-energy, dipole-moment, and transition-moment functions for the ground and lowest nine excited states of NaAr are calculated employing multireference configuration interaction (MRCI) from complete-active-space self-consistent-field (CASSCF) wave functions in large Gaussian atomic basis sets [14] supplemented with suitable diffuse functions. The NaAr potential-energy curves and selected dipole and transition moments so obtained are highlighted elsewhere in these proceedings [1]. Similar calculations for AlAr are in progress; preliminary results obtained employing MRCI from selected CASSCF configurations are shown in another abstract in this volume [2].…”

Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 87%

“…Similar calculations for AlAr are in progress; preliminary results obtained employing MRCI from selected CASSCF configurations are shown in another abstract in this volume [2]. These data are used directly in computational implementations of the spectral theory and in ensuing simulations of the structures and absorption spectra of NaAr" and AlAr" clusters [ 1,2].…”

Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 94%

“…The spectral theory of chemical binding, which has been under development for about two years [8,9], aims to provide accurate electronic potential-energy surfaces for such aggregates, which in turn reveal their structural and spectroscopic properties, as well as information related to their stabilities and reactivities. Details of the theoretical approach are provided elsewhere in these proceedings [1,2], but its key features are as follows: (1) it treats physical and chemical binding on a common basis; (2) it gives a rigorous theoretical foundation for a class of methods, loosely known as "atoms-in-molecules" or "diatomics-in-molecules" aproaches, which build potential surfaces from information related to component fragments [10][11][12]; (3) it requires only diatomic molecule calculations from conventional quantum chemistry, and these can be performed once and for all for any pair of atoms; and (4) it is potentially applicable to systems of 1000 or more atoms.…”

Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 99%

“…Thirdly, the structures, spectra, and thermodynamic properties of proposed and synthesized new oxidizers, fuels, and monopropellants are also being calculated. An overview and highlights of these efforts are presented in this report, with farther details on specific topics provided in other contributions to these proceedings [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Theoretical Investigations of HEDM

Sheehy¹

1998

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Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 87%

Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 94%

Section: Spectral Theory Of Chemical Bindingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Theoretical Investigations of HEDM

Sheehy¹

1998

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“…An attractive alternative approach, potentially capable of overcoming the aforementioned limitations, is based on enforcing the antisymmetry requirements of Pauli’s principle “ex-post-facto” by unitary transformation of a Hamiltonian matrix which is considerably simpler to evaluate than those of conventional developments, also offering additional flexibility in choice of forms of product representations employed for this purpose. − In the case of simple atomic- or molecular-orbital representations in Hartree-product forms, for example, it has been shown that results identical with conventional use of Slater determinants are obtained, employing either finite or arbitrarily large orbital basis sets, and adding confidence to the approach, but not providing any particular computational advantage in orbital-product cases. By contrast, use of Hartree-like products of universal many-electron atomic eigenstates as an orthonormal representation for purposes of analysis and for support suitable for molecular computations, as described in the original formulation of the method, , has led to a continuing series of investigations in clarification of aspects of the theory, ,,− , and for purposes of implementation. ,,,, These developments also incorporate in a unified ab initio formalism earlier attempts to employ atomic-based representations in combined descriptions of van der Waals and chemical forces, semiempirical “atoms-in-molecules” calculations of chemical bond strengths, adoption of atomic-pair energies in semiempirical “diatomics-in-molecules” approximations to potential energy surfaces, and clarification of the role of electron permutation symmetry in long-range atomic interactions. , …”

Section: Introductionmentioning

confidence: 99%

Atomic Spectral Methods for Ab Initio Molecular Electronic Energy Surfaces: Transitioning From Small-Molecule to Biomolecular-Suitable Approaches

et al. 2016

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Continuing attention has addressed incorportation of the electronically dynamical attributes of biomolecules in the largely static first-generation molecular-mechanical force fields commonly employed in molecular-dynamics simulations. We describe here a universal quantum-mechanical approach to calculations of the electronic energy surfaces of both small molecules and large aggregates on a common basis which can include such electronic attributes, and which also seems well-suited to adaptation in ab initio molecular-dynamics applications. In contrast to the more familiar orbital-product-based methodologies employed in traditional small-molecule computational quantum chemistry, the present approach is based on an "ex-post-facto" method in which Hamiltonian matrices are evaluated prior to wave function antisymmetrization, implemented here in the support of a Hilbert space of orthonormal products of many-electron atomic spectral eigenstates familiar from the van der Waals theory of long-range interactions. The general theory in its various forms incorporates the early semiempirical atoms- and diatomics-in-molecules approaches of Moffitt, Ellison, Tully, Kuntz, and others in a comprehensive mathematical setting, and generalizes the developments of Eisenschitz, London, Claverie, and others addressing electron permutation symmetry adaptation issues, completing these early attempts to treat van der Waals and chemical forces on a common basis. Exact expressions are obtained for molecular Hamiltonian matrices and for associated energy eigenvalues as sums of separate atomic and interaction-energy terms, similar in this respect to the forms of classical force fields. The latter representation is seen to also provide a long-missing general definition of the energies of individual atoms and of their interactions within molecules and matter free from subjective additional constraints. A computer code suite is described for calculations of the many-electron atomic eigenspectra and the pairwise-atomic Hamiltonian matrices required for practical applications. These matrices can be retained as functions of scalar atomic-pair separations and employed in assembling aggregate Hamiltonian matrices, with Wigner rotation matrices providing analytical representations of their angular degrees of freedom. In this way, ab initio potential energy surfaces are obtained in the complete absence of repeated evaluations and transformations of the one- and two-electron integrals at different molecular geometries required in most ab inito molecular calculations, with large Hamiltonian matrix assembly simplified and explicit diagonalizations avoided employing partitioning and Brillouin-Wigner or Rayleigh-Schrödinger perturbation theory. Illustrative applications of the important components of the formalism, selected aspects of the scaling of the approach, and aspects of "on-the-fly" interfaces with Monte Carlo and molecular-dynamics methods are described in anticipation of subsequent applications to biomolecules and other large aggregates.

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Spectral Theory of Physical and Chemical Binding: Aspects of Computational Implementation

Cited by 2 publications

References 10 publications

Theoretical Investigations of HEDM

Theoretical Investigations of HEDM

Atomic Spectral Methods for Ab Initio Molecular Electronic Energy Surfaces: Transitioning From Small-Molecule to Biomolecular-Suitable Approaches

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