Theoretical studies of possible high energy density materials

Ab initio quantum chemistry methods are applied to possible high energy density materials (HEDM). The candidate molecules are investigated for their structures, energetics, stabilities, nature of bonding, and other properties. The investigation of molecules of interest includes: (1) stabilities and bonding of NH[subscript]4[superscript]- and PH[subscript]4[superscript]-, decomposition paths using dynamic reaction coordinates for tetrahedral isomers and their ionization potentials; (2) aromaticity associated with inorganic benzene, X[subscript]3Y[subscript]3H[subscript]6 where X and Y are chosen from Zn, B, Al, Ga, C, Si, Ge, N, P, As, O and S such that there are total of six [pi] electrons, by examining their configuration interaction density matrices; (3) stabilities and energetics of inorganic prismanes, X[subscript]3Y[subscript]3H[subscript]6 where X and Y are chosen from B, Al, Ga, C, Si, Ge, N, P and As, and the bonding of these molecules examined by total electron density analysis and localized orbitals; (4) potential energy surface of boron-nitrogen prismane and its possible decomposition paths;Non-adiabatic interaction is examined for XH[subscript]2, where X is chosen from C, Si, Ge, Sn and Pb. Spin-orbit coupling using the Breit-Pauli hamiltonian is used to mix the lowest singlet and triplet states

Stabilities and Energetics of Inorganic Benzene Isomers: Prismanes

Ab initio calculations of inorganic prismanes, with the formula (XH-YH) 3, where X = B, AI, and Ga and Y = N, P, and As, as well as X or Y = C, Si, and Ge, were carried out. Energetics of these species are compared with those of the planar benzene analog and chair/boat conformers. The prismane and planar structures containing first period elements (B, C, and N) are all stable (i.e. minima on the potential energy surfaces). Chair and boat conformers are potential energy minima only in compounds containing second or third period elements. For those species with a first period element in the 1, 3, 5 positions, the planar benzene-like structure is the global minumum; otherwise, the planar structure is not a minimum. The lowest minimum found is the prismane arrangement for Si6H6 and Ge~6 and the chair structure for ShGe3H6. Other molecules have distorted minima

Relativistic Potential Energy Surfaces of XH2 (X=C, Si, Ge, Sn, and Pb) Molecules: Coupling of 1 A 1 and 3 B 1 States

Potential energy surfaces of the 1 A 1 and 3 B 1 states for XH2 molecules (X=C, Si, Ge, Sn, Pb) are investigated with ab initio full valence multiconfigurational self‐consistent field wave functions, using effective core potentials. Spin–orbit coupling is also calculated to construct relativistic potential energy surfaces. The relativistic potential energy surfaces are compared with the adiabatic nonrelativistic potentials. Simple one dimensional Landau–Zener transition probabilities are calculated at the minimum energy crossing points of XH2 molecules to estimate the intersystem crossing probability

Main Group Effective Nuclear Charges for Spin-Orbit Calculations

The effective nuclear charges (Z.,ff), which are empirical parameters in an approximate spin-orbit Hamiltonian, are determined for main group elements in the second to fifth periods by using experimental results for the fine structure splittings (FSS) in II states of diatomic hydrides. All calculations use full valence multiconfiguration self-consistent field (MCSCF) wave functions with the effective core potential (ECP) basis sets proposed by Stevens et al., augmented by one set of polarization functions. These effective nuclear charges are tested by predicting the FSS in many diatomic molecules and are then applied to evaluate the relativistic potential energy curves of the methylene analogs AHz (A = C, Si, Ge, and Sn), as well as XHX and NaX (X = Br and 1)

Effects of Conjugation and Aromaticity on the Sulfoxide Bond

An ab initio computational study on a series of sulfoxides is reported. The SO bond dissociation energy (BDE) of sulfoxides in which the sulfur atom is included in a formally aromatic ring (e.g., thiophene sulfoxide) is found to be decreased by as much as 25 kcal/mol, compared to DMSO. A complementary effect is observed for sulfoxides in which the sulfur is included in a formally antiaromatic ring (e.g., thiirene sulfoxide), in which SO BDEs are increased by as much as 15 kcal/mol. Both effects are attenuated by benzannulation. Examination of calculated geometries and isodesmic reactions with pure hydrocarbons leads to the conclusion that the observed effects are due to a severe disruption of the (anti) aromaticity of the sulfur-containing ring on oxidation. The cyclic sulfoxides appear to be neither significantly aromatic nor antiaromatic by energetic considerations. No significant SO bond strength effect is observed for simple conjugation. Inversion barriers for several sulfoxides are also calculated

Accurate Ab Initio Potential Energy Curve of F2. II. Core-valence Correlations, Relativistic Contributions, and Long-Range Interactions

The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F2molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spin-orbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion

Applications of Parallel GAMESS

In this paper we discuss several recent applications that would have been difficult or impossible without the availability of the parallel implementation of the electronic structure code GAMESS. These applications include the study of highly strained rings, such as inorganic prismanes and bicyclobutanes, cage compounds such as cyclophanes and atranes, the neutral \u3c-\u3e zwitterion isomerization of glycine, transition metal-main group binding, and the implementation of parallel graphics

Theoretical studies of possible high energy density materials

Ab initio quantum chemistry methods are applied to possible high energy density materials (HEDM). The candidate molecules are investigated for their structures, energetics, stabilities, nature of bonding, and other properties. The investigation of molecules of interest includes: (1) stabilities and bonding of NH[subscript]4[superscript]- and PH[subscript]4[superscript]-, decomposition paths using dynamic reaction coordinates for tetrahedral isomers and their ionization potentials; (2) aromaticity associated with inorganic benzene, X[subscript]3Y[subscript]3H[subscript]6 where X and Y are chosen from Zn, B, Al, Ga, C, Si, Ge, N, P, As, O and S such that there are total of six [pi] electrons, by examining their configuration interaction density matrices; (3) stabilities and energetics of inorganic prismanes, X[subscript]3Y[subscript]3H[subscript]6 where X and Y are chosen from B, Al, Ga, C, Si, Ge, N, P and As, and the bonding of these molecules examined by total electron density analysis and localized orbitals; (4) potential energy surface of boron-nitrogen prismane and its possible decomposition paths;Non-adiabatic interaction is examined for XH[subscript]2, where X is chosen from C, Si, Ge, Sn and Pb. Spin-orbit coupling using the Breit-Pauli hamiltonian is used to mix the lowest singlet and triplet states.</p

Stabilities and Energetics of Inorganic Benzene Isomers: Prismanes

Ab initio calculations of inorganic prismanes, with the formula (XH-YH) 3, where X = B, AI, and Ga and Y = N, P, and As, as well as X or Y = C, Si, and Ge, were carried out. Energetics of these species are compared with those of the planar benzene analog and chair/boat conformers. The prismane and planar structures containing first period elements (B, C, and N) are all stable (i.e. minima on the potential energy surfaces). Chair and boat conformers are potential energy minima only in compounds containing second or third period elements. For those species with a first period element in the 1, 3, 5 positions, the planar benzene-like structure is the global minumum; otherwise, the planar structure is not a minimum. The lowest minimum found is the prismane arrangement for Si6H6 and Ge~6 and the chair structure for ShGe3H6. Other molecules have distorted minima.Reprinted (adapted) with permission from Journal of the American Chemical Society 116 (1994): 11407, doi:10.1021/ja00104a021. Copyright 1994 American Chemical Society.</p

A Theoretical Study of NH4- and PH4-

The potential energy surfaces of ~- and P~- were investigated using ab initio electronic structure calculations. Additivity of correlation and basis set effects was used to estimate relative energies. The tetrahedral structures of N~- and P~- are predicted to be minima on the respective potential energy surfaces. Ab initio classical trajectory calculations were carried out in order to elucidate possible dissociation paths of tetrahedral ions. The dissociation barrier was estimated to be 32.5 kcaVmol for N~- and 5.5 kcaVmol for p~-. Ionization potentials for the tetrahedral structures of N~- and p~- were calculated to be 0.39 and 0.32 eV, respectively.Reprinted (adapted) with permission from Journal of Physical Chemistry 99 (1995): 12773, doi:10.1021/j100034a014. Copyright 1995 American Chemical Society.</p