Monte Carlo calculation of the potential energy surface for octahedral confined H$$_2^+$$2+

Abstract

A rich literature has been produced on the quantum states of atoms and molecules confined into infinite potential wells with a specified symmetry. Apart from their interest as basic quantum systems, confined atoms and molecules are useful models for extreme high pressure states of matter, spectroscopically active defects in solid lattices and chemical species in molecular cages. A most important case is that of H + 2 for which little or no results are available in the case of polyhedral confinement. The approach of the authors makes use of the Diffusion Monte Carlo (DMC) method. The advantage of this method is that previously developed codes are readily adapted to new, even complex, well geometries and nuclear positions. In this paper the potential energy surface (PES) of H + 2 confined inside an octahedral well is reported for restricted D 4h and D 3d geometries and different well widths. The results are discussed using the concept of electron compression and the correlation with semi-confined atomic orbitals.

A database approach for materials selection for hydrogen storage in aerospace technology

“…of materials in the framework of the ESA project "Challenges related to the design of a reservoir for the transport of H 2 " (including metal hydrides, organic liquids and MOFs), the model database presented and discussed here considers clathrates as good candidates in the context of aerospace applications as a fully detailed example. The present implementation is a demonstration, and future ones may make use of more advanced data such as those related to the quantum state of nanoconfined hydrogen species (Longo et al 2018) and the kinetics of such species, also in their excited states (Longo et al 2011;Esposito 2019;Coppola et al 2016). Furthermore, molecular dynamics studies may help to test the limit of the Arrhernius Law in systems kinetics (Aquilanti et al 2018).…”

Stochastic models of systems for Nanotechnology: from micro to macro scale

“…On this basis, in recent years we have developed a suite of Diffusion Monte Carlo codes designed for the study of hydrogen-based and nano species confined by infinite potential wells of various geometries [Micca Longo, 2015a;Micca Longo, 2015b;Micca Longo, 2015c;Longo, 2018]. In contrast with previous Monte Carlo calculations [Sarsa, 2012], our programs do not employ an analytic guess wavefunctions to reduce variance by the importance sampling technique.…”

“…A recent result (figures 1(c), (d)) concerns the first calculation of the PESs of the + H 2 ion confined in an octahedral potential well, which describes the quantum state of this species in real crystal lattice cavities much better than a spherical or ellipsoidal potential well (Longo et al 2018). In this case, the PES is quite complex since it depends not only on the internuclear distance but also on the orientation of the molecular axis into the well.…”

Compressed hydrogen atoms confined within generic boxes

“…The radial part of the wave function in such a spherical box can be written in terms of hypergeometric functions, the roots of which may then be calculated to obtain numerical values for the hydrogen energy spectrum [3,4,19–22]. Although most effort has been focused on spherical boxes, there have been studies focused on other box geometries, including spheroids [23], cylinders [24], cubes [25,26] and certain polyhedra [27,28]. Others have studied the problem of off-centre hydrogen, where the nucleus is not located at the centre of the box [29,30]; the resulting asymmetry in the nucleus shifts the energy spectrum.…”