Ab initio many-body calculations of static dipole polarizabilities of linear carbon chains and chain-like boron clusters

In this paper we report a theoretical study of the static dipole polarizability of two one-dimensional structures: (a) linear carbon chains C$_{n} (n=2-10)$ and (b) ladder-like planar boron chains B$_{n} (n=4-14)$. The polarizabilities of these chains are calculated both at the Hartree-Fock and the correlated level by applying accurate ab initio quantum chemical methods. Methods such as restricted Hartree-Fock, multi-configuration self-consistent field, multi-reference configuration-interaction method, M{\o}ller-Plesset second-order perturbation theory, and coupled-cluster singles, doubles and triples level of theory were employed. Results obtained from ab initio wave-function-based methods are compared with the ones obtained from the density-functional theory. For the clusters studied, directionally averaged polarizability per atom for both the systems is seen to increase with the chain size.Comment: 9 pages, 3 figures (included

Correlated ground state ab initio studies of polymers

In this thesis we have investigated the correlated ground state properties of polymers by applying wave-function-based ab-initio quantum-chemical methods such as the Hartree-Fock approach, the full configuration interaction method (FCI), coupled-cluster (CC) and Moller-Plesset second-order perturbation (MP2) theory. The polymers we have studied are the boron-nitrogen polymers, i.e., polyiminoborane (PIB) and polyaminoborane (PAB), the lithium hydride chain and the beryllium hydride polymer as well as the polymethineimine (PMI). The optimized structural parameters, cohesive energies, polymerization ernergies, relative stabilities of isomeric forms and some band structure results are presented. The results demonstrated that quantum chemical ab initio methods can be applied successfully to infinite systems like polymers, although such calculations are still far from being routine

Ab initio many-body calculations on infinite carbon and boron-nitrogen chains

In this paper we report first-principles calculations on the ground-state electronic structure of two infinite one-dimensional systems: (a) a chain of carbon atoms and (b) a chain of alternating boron and nitrogen atoms. Meanfield results were obtained using the restricted Hartree-Fock approach, while the many-body effects were taken into account by second-order M{\o}ller-Plesset perturbation theory and the coupled-cluster approach. The calculations were performed using 6-31$G^{**}$ basis sets, including the d-type polarization functions. Both at the Hartree-Fock (HF) and the correlated levels we find that the infinite carbon chain exhibits bond alternation with alternating single and triple bonds, while the boron-nitrogen chain exhibits equidistant bonds. In addition, we also performed density-functional-theory-based local density approximation (LDA) calculations on the infinite carbon chain using the same basis set. Our LDA results, in contradiction to our HF and correlated results, predict a very small bond alternation. Based upon our LDA results for the carbon chain, which are in agreement with an earlier LDA calculation calculation [ E.J. Bylaska, J.H. Weare, and R. Kawai, Phys. Rev. B 58, R7488 (1998).], we conclude that the LDA significantly underestimates Peierls distortion. This emphasizes that the inclusion of many-particle effects is very important for the correct description of Peierls distortion in one-dimensional systems.Comment: 3 figures (included). To appear in Phys. Rev.

Correlated ground state ab initio studies of polymers

In this thesis we have investigated the correlated ground state properties of polymers by applying wave-function-based ab-initio quantum-chemical methods such as the Hartree-Fock approach, the full configuration interaction method (FCI), coupled-cluster (CC) and Moller-Plesset second-order perturbation (MP2) theory. The polymers we have studied are the boron-nitrogen polymers, i.e., polyiminoborane (PIB) and polyaminoborane (PAB), the lithium hydride chain and the beryllium hydride polymer as well as the polymethineimine (PMI). The optimized structural parameters, cohesive energies, polymerization ernergies, relative stabilities of isomeric forms and some band structure results are presented. The results demonstrated that quantum chemical ab initio methods can be applied successfully to infinite systems like polymers, although such calculations are still far from being routine

Correlated ground state ab initio studies of polymers

In this thesis we have investigated the correlated ground state properties of polymers by applying wave-function-based ab-initio quantum-chemical methods such as the Hartree-Fock approach, the full configuration interaction method (FCI), coupled-cluster (CC) and Moller-Plesset second-order perturbation (MP2) theory. The polymers we have studied are the boron-nitrogen polymers, i.e., polyiminoborane (PIB) and polyaminoborane (PAB), the lithium hydride chain and the beryllium hydride polymer as well as the polymethineimine (PMI). The optimized structural parameters, cohesive energies, polymerization ernergies, relative stabilities of isomeric forms and some band structure results are presented. The results demonstrated that quantum chemical ab initio methods can be applied successfully to infinite systems like polymers, although such calculations are still far from being routine

Ab initio treatment of electron correlations in polymers: lithium hydride chain and beryllium hydride polymer

Correlated ab initio electronic structure calculations are reported for the polymers lithium hydride chain [LiH] ∞ and beryllium hydride [Be2H4]∞. First, employing a Wannier-function-based approach, the systems are studied at the Hartree-Fock level, by considering chains, simulating the infinite polymers. Subsequently, for the model system [LiH]∞, the correlation effects are computed by considering virtual excitations from the occupied Hartree-Fock Wannier functions of the infinite chain into the complementary space of localized unoccupied orbitals, employing a full-configuration-interaction scheme. For [Be2H4]∞, however, the electron correlation contributions to its ground state energy are calculated by considering finite clusters of increasing size modelling the system. Methods such as Møller–Plesset second–order perturbation theory and coupled–cluster singles, doubles and triples level of theory were employed. Equilibrium geometry, cohesive energy and polymerization energy are presented for both polymers, and the rapid convergence of electron correlation effects, when based upon a localized orbital scheme, is demonstrated. I