On the dual deuterium/deuteron nature of D charge distribution in the Ti host matrix: a DFT analysis

In the present work we have investigated the charge distribution on deuterium atom inside a titanium host matrix and their interaction energy. This analysis is motivated by the role that Ti-D alloys play in nuclear processes, i.e. the reported neutron generation as a consequence of the pressure exerted on such hybrid systems. A two-fold DFT procedure has been employed in order to carry out our analysis, namely a periodic and a cluster approach. Both show that the D atom, at variance with the prediction by T. Asami et al. (T. Asami, Journal of Condensed Matter Nuclear Science 2011; 5:7-16; T Asami, N. Sano, Journal of Condensed Matter Nuclear Science 2012; 9:1-9), tends to avoid the deuteron form when entering the Ti tetrahedral site. In particular, according to the cluster approach results, both the Voronoi Deformation Density atomic charge analysis and the interaction energy decomposition analysis indicate that the deuterium enters the tetrahedron cage retaining its electron, provided that a high energy barrier could be overcome. The largest contribution to the interaction energy is the charge-transfer orbital interaction term but the sizeable energy barrier is mainly due to the electrostatic repulsive interaction between Ti cluster and D+. We thus conclude that the experimental conditions (i.e., the combination of pressure and temperature) could be responsible for the hypothesized "switching on" of the deuterium-to-deuteron charge oxidation.