Structure, spectroscopy and electronic properties of neutral lattice-like (MgO) n clusters: a study based on a blending of DFT with stochastic algorithms inspired by natural processes

Energetics and spectroscopic studies of CNO (-) (H 2 O) n $$ {\mathbf{CNO}}^{\left(\hbox{-} \right)}{\left({\mathbf{H}}_{\mathbf{2}}\mathbf{O}\right)}_{\mathbf{n}} $$ clusters and the temperature dependencies of the isomers: An approach based on a combined recipe of parallel tempering and quantum chemical methods

A system associated with several number of weak interactions supports numerous number of stable structures within a narrow range of energy. Often, a deterministic search method fails to locate the global minimum geometry as well as important local minimum isomers for such systems. Therefore, in this work, the stochastic search technique, namely parallel tempering, has been executed on the quantum chemical surface of theCNO (-) (H 2 O) n $$ {\mathrm{CNO}}^{\left(\hbox{-} \right)}{\left({\mathrm{H}}_2\mathrm{O}\right)}_n $$ system forn = 1 $$ n=1 $$ -8 to generate global minimum as well as several number of local minimum isomers. IR spectrum can act as the fingerprint property for such system to be identified. Thus, IR spectroscopic features have also been included in this work. Vertical detachment energy has also been calculated to obtain clear information about number of water molecules in several spheres around the central anion. In addition, in a real experimental scenario, not only the global but also the local minimum isomers play an important role in determining the average value of a particular physically observable property. Therefore, the relative conformational populations have been determined for all the evaluated structures for the temperature range between 20K and 400K. Further to understand the phase change behavior, the configurational heat capacities have also been calculated for different sizes.

Structure elucidation and construction of isomerisation pathways in small to moderate-sized (6-27) MgO nanoclusters: an adaptive mutation simulated annealing based analysis with quantum chemical calculations

Determination of global minimum structures and elucidation of reaction paths or minimum energy paths between low-lying minima are of great chemical importance. To that end, we have used our own Adaptive Mutation Simulated Annealing method to determine the global minimum and the minimum energy paths for various isomerisation reactions for small to moderate-sized (MgO)n (n = 6-27) clusters, using the Born-Mayer potential with suitable parameter values. The minimum energy structures obtained by us match well with previously reported data and are used as guess structures for further optimisation at the DFT level (using the B3LYP functional and DGDZVP basis set). Our optimised structures are found to match very well with the further DFT optimised structures, where the comparison is done by determining the root mean square deviation values as well as the radial distribution function profiles. A scheme is proposed to determine the minimum energy paths for isomerisation reactions for some cluster sizes where the transition state/s obtained by us, at very low computational cost, match well with those obtained from further optimisation using DFT calculations. We have shown the efficacy of our method in determining the reaction pathways, even for cases that involve multi-step reactions.

Electronic and vibrational second hyperpolarizabilities of (MgO)n clusters

In this work, we report results for the static second hyperpolarizability of magnesium oxide clusters including electronic and vibrational contributions. The comparison between second-order Møller-Plesset (MP2) perturbation theory and coupled cluster results to the electronic contribution points out that MP2 is a suitable method to compute this property. When computed at the MP2 level, the electronic contribution per atom converges to approximately 5000 a.u. Vibrational corrections were computed at the MP2 level through the perturbation theoretical method of Bishop and Kirtman. Results obtained showed that the term [α²]^0,0 represents around 20% of the electronic counterpart while the term [μβ]^0,0 is comparable to it. Modes that contribute significantly to [α²]^0,0 are those in which all or part of the bond lengths simultaneously increase and decrease, leading to large polarizability derivatives. In turn, modes that provide relevant contributions to [μβ]^0,0 are those in which oxygen anions move in opposite directions to the magnesium cations yielding large derivatives of the dipole moment and first hyperpolarizability.

Interaction of magnesium hydride clusters with Nb doped MgO additive studied by density functional calculations

The hydrogen adsorption behaviour of MgO differs significantly to that of Nb doped MgO, draws new promising applications in hydrogen storage and catalysis.