R. Pis Diez

A conformational study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane using molecular dynamics and density functional theory

Abstract A theoretical study of the conformational space of the cyclic diperoxide 3,3,6,6-tetramethyl-1,2,4,5-tetroxane is presented in this work. Molecular dynamics simulations are performed to scan the conformational space of the molecule. Density functional calculations are carried out on the stable conformers to get a better description of molecular geometries and total energy differences. The conformers are properly characterized by means of a vibrational analysis after geometry optimization. Further, a natural bond orbital analysis is used to shed light into the relative stability of the different stable conformers.

A density functional study of small NixSn clusters with x=1–4

Abstract Results of a systematic study of the geometry, electronic structure, magnetic, and vibrational properties of small NixSn clusters, with x=1–4, within the framework of the density functional theory are presented in this work. Population analyses are used to investigate the effect of tin on the nickel atoms towards an understanding of the changes in the catalytic behavior observed in the bimetallic system when it is compared with pure nickel.

A density functional study of the Ni5Sn and Ni6Sn clusters

Abstract A systematic study of the geometric, electronic, and vibrational properties of the Ni 5 Sn and Ni 6 Sn clusters using both the local and the gradient-corrected approximations to the density functional theory is presented in this work. The ionisation potentials and electron affinities are also calculated for the stable neutral clusters. Population analyses are used to investigate charge transfer process within the neutral and ionised clusters. Moreover, the changes in the sp and d populations of the nickel atoms are used to discuss the possible catalytic behaviour of the neutral clusters towards capture and dissociation of dihydrogen. The results are compared with the well-known lack of activity towards the activation of the H–H bond in H 2 undergone by Ni–Sn bimetallic catalysts.

A density functional study of the ionisation potentials and electron affinities of small NixSn clusters with x=1–4

Abstract The ionisation potentials and electron affinities of NinSn clusters, with n=1–4, were investigated within the framework of the local spin density and the generalized gradient approximations of the density functional theory. The change in the geometric parameters of the ionized clusters after geometry and spin multiplicity optimisation is discussed. The electronic charge rearrangement undergone by the atoms in the clusters are also presented and discussed. Finally, a relationship is proposed among the ionisation processes under study and the possible catalytic activity of the NinSn clusters.

Using hydrogen atoms to terminate zeolite clusters: A semiempirical study

Abstract The use of H atoms to terminate zeolite clusters is studied in the present work using the semiempirical MNDO method. It is shown that some properties, such as Mulliken atomic charges, depend on the Si–H distance. It is also shown that the dependence is very smooth within a given range of Si–H distances. Thus, the useful concept of a universal Si–H distance when finite models are used to represent zeolitic materials arises naturally.