Demetrios Xenides

Polarizability evolution on natural and artificial low dimensional binary semiconductor systems: A case study of stoichiometric aluminum phosphide semiconductor clusters.

The dependences of the static dipole polarizabilities per atom (PPAs) on the bonding and shape of selected stoichiometric aluminum phosphide clusters (ground states and higher lying species) of small and medium sizes have been comprehensively studied at Hartree-Fock and the second order Moller-Plesset perturbation levels of theory. It is shown that the nonmonotonic size variations in the mean PPAs of AlP species which maintain closed cagelike structures, frequently observed in clusters, are directly related to covalent homoatomic bonds inside each clusters framework. Accordingly, the PPAs of clusters which are characterized by one or more bonds between the Al and P atoms are larger than the PPAs of clusters with the uniform alternating Al-P bond matrix. This is caused by the electron transfer increase from the electropositive Al to the electronegative P atom with the cluster growth. This transfer is larger for the clusters characterized by alternating Al-P bonding. The later effect explains the decrease in the PPA of AlP species which maintain closed cage-like structures, with the cluster growth. However, this picture drastically changes for artificial metastable prolate species built up by the ground states of smaller clusters. It is demonstrated that for prolate binary AlP clusters of medium size, the shape dominates against any other structural or bonding factor, forcing the PPA to increase with the cluster size. Nonetheless, as the cluster size grows, it is predicted that the PPAs of the studied prolate clusters will saturate eventually with the cluster size. Also, it is verified that the theoretical predicted polarizabilities of AlP semiconductor clusters are larger than the bulk polarizability in accord with other theoretical predictions for similar systems. Lastly, it is pointed out that major bonding or structural changes should take place in order the convergence with the bulk polarizability to be accomplished since it is revealed that the size increase is a necessary but not a sufficient factor for the cluster to bulk transition.

Electric polarizability and hyperpolarizability of BrCl(X1Σ

We have obtained accurate static dipole polarizabilities and hyperpolarizabilities for BrCl from finite-field Moller–Plesset perturbation theory and coupled cluster calculations. Our best values for the dipole properties have been obtained at the CCSD(T) level of theory with a large [6s5p5d2f1g/5s4p4d2f1g] basis set and are dipole moment μ/ea0 = −0.1778, mean dipole polarizability and anisotropy Δα/e2a20Eh−1 = 20.44, mean first hyperpolarizability and second hyperpolarizability . At the same level of theory and with a [6s5p4d1f/5s4p3d1f] basis set, the above properties vary around the experimental bond length Re = 2.136 065 A as

Preface of the “Computational quantum chemistry and from small clusters to functional building blocks of novel nanomaterials symposium”

This symposium included papers with emphasis on Theoretical and Computational Quantum Chemistry and special focus on Materials Science perspectives.

Computational Quantum Chemistry: From Atoms and Molecules to Clusters and Nano‐objects

This symposium on Computational Quantum Chemistry attracted 36 papers and included a special session on electric polarizability.

Finding the Pattern in the Space of ab initio and DFT Theoretical Descriptions: A Pattern Recognition and Metric Space Approach Based on the Electric Response Properties of the Open and Ring Isomers of XO2 (X = O,S)

A test set of four molecules was formed by considering the bonding in the open (C2v) and ring (D3h) forms of ozone, and the open and ring isomers of sulfur dioxide (both of C2v symmetry). This test set was used as to assess the performance of various Density Functional Theory (DFT) methods in (hyper)polarizability calculations against well established ab initio methods. The analysis is aided by arguments chosen from the information theory, graph theory and pattern recognition fields of Mathematics: The multidimensional space is formed by the methods which are playing the role of vectors with the independent components of the electric properties to act as the coordinates of these vectors, hence the relation between different vectors (e.g., methods) can be quantified by a proximity measure. Results are in agreement with previous studies revealing the acceptable and consistent behavior of the mPW1PW91, B3P86 and PBE1PBE methods. We note the remarkable good performance of the B2PLYP and mPW2PLYP functionals w...

Electric Dipole Polarizability of Aluminum Phosphide Clusters AlnPn (n = 2–9) and Electron Delocalization

We have calculated the static dipole polarizabilities of stoichiometric AlnPn clusters with n = 2–9 at HF, B3LYP, B3PW91 and mPW1PW91 levels of theory using basis sets of increasing size. Our results show that AIP clusters behave like the well studied GaAs clusters and their per‐atom polarizabilities decrease rapidly with cluster size. At HF and the DFT levels the per‐atom‐mean polarizability saturates with size after n = 4. Finally, from the methodological viewpoint, our results show that for those clusters, the different hybrid density functionals we used converge in the computation of the per‐atom‐mean polarizability as the size of the cluster increases.We have calculated the static dipole polarizabilities of stoichiometric AlnPn clusters with n = 2–9 at HF, B3LYP, B3PW91 and mPW1PW91 levels of theory using basis sets of increasing size. Our results show that AIP clusters behave like the well studied GaAs clusters and their per‐atom polarizabilities decrease rapidly with cluster size. At HF and the DFT levels the per‐atom‐mean polarizability saturates with size after n = 4. Finally, from the methodological viewpoint, our results show that for those clusters, the different hybrid density functionals we used converge in the computation of the per‐atom‐mean polarizability as the size of the cluster increases.

Ab Initio QM/MM Simulations of Water and Hydrated Cations

An overview of the recent advances in ab initio simulations of liquid water and aqueous systems containing cations is given. In both cases a spherical region containing a central species (water molecule or ion, respectively) surrounded by a all nearest water molecules (coordination shell(s)) is treated quantum mechanically, i.e. at the Hartree‐Fock level. Structural and dynamical insights are described by the O–O and M+–O (M = Metal) interactions, via the respective radial distribution functions and the velocity autocorrelation functions, respectively. This evaluation enables (i) the estimation of the number and the lifetime of the hydrogen bonds in liquid water, (ii) the definition of the hydration shell(s) of the cations, and (iii) the characterization of ions as either chaotropic or kosmotropic.