## 1 Introduction  
Hydrogen is a non-polluting fuel, and it is viewed as a promising substitute for fossil fuels and clean fuel that might be on the horizon. When it ignites, it simply conveys water vapour into the atmosphere, not in any way like non-sustainable power sources, such as oil, vaporous petroleum, and coal, i.e., fuels that contain carbon and produce carbon dioxide (CO\({}_{2}\)) or carbon monoxide (CO), including a higher extent of carbon outpourings, nitrogen oxides (NO\({}_{3}\)), and sulphur dioxide (SO\({}_{2}\)). Non-sustainable power sources, in a like manner, release ash particles into the earth, which is significantly contributing to global warming. Global warming has also risen to severe levels due to huge emissions of CO\({}_{2}\) into the atmosphere due to the heavy dependence of people on limited fossil fuels as energy resources [1; 2; 3]. Among several alternative fuel sources, hydrogen (H\({}_{2}\)) has gained focus because it provides primary advantages and meets ideal fuel requirements [4], and is also one of the most promising and vital fuels for the future [5]. Hydrogen is great, significantly copious, and renewable, economical fuel and packs imperativeness per unit mass like some other exorbitant empowers. H\({}_{2}\) can be used for power generation, transportation and heating as a highly efficient fuel [6]. The major issue with this fuel is its storage, since it ought to be taken care of like other compacted gases. Hydrogen is regularly stored in three methods, i.e., compression, liquefaction (changing the phase from gas to liquid), and as a solid material [7; 8]. Clathrate hydrates are inclusion compounds which incorporate guest molecules inside the polyhedral cages of the host framework, which is made up of hydrogen-bonded water molecules [9]. Within the clathrate lattice, water molecules form a network of hydrogen-bonded cavity structures that enclose the guests, the latter generally comprisingsingle or mixed low-molecular-diameter gases and/or organic compounds (e.g., methane, tetrahydrofuran(THF)) [10; 11; 12; 13; 14; 15]. In recent years, clathrate hydrates have generated much interest in the study of hydrogen storage, as a possible future energy-storage medium. Molecular dynamics (MD) has been significant in advancing our understanding in hydrate science at the atomistic level of insight. This has added to our understanding of clathrate hydrates' thermodynamic properties and their possibilities for energy stockpiling, especially of hydrogen. Indeed, these MD methodologies might be deployed to a greater degree in the coming decade, as what appears computationally 'heroic' today may turn out to be routinely available in the hydrate simulation network in the medium-term future [16; 17; 18]. During much of the 20 th century, it had been suspected that the molecular size of hydrogen was too small to confer appreciable thermodynamic stabilisation to clathrate hydrates [10; 19], although more recent investigations in the past 20 years or so show that a large degree of H\({}_{2}\) (perhaps up to around 5 wt %, albeit with some uncertainty) can be accommodated in cubic structure II clathrate hydrates under higher-pressure conditions (i.e., at pressures of around 1 GPa and higher at ambient temperature conditions) [20; 21]. Understandably, this revelation has provoked significant examination into clathrate hydrates as potential hydrogen storage materials [20; 21; 22; 23; 24]. Given this great, and well-justified, interest in hydrogen hydrates as a hydrogen-storage material, in the present study, we are motivated by unresolved, open questions pertaining to both H2 inter-cage diffusivity and cage occupancies, which have a substantial bearing on hydrates as a viable energy-storage medium. Inter-cage hopping is a phenomenon in which the guest molecule (D\({}_{2}\) or H\({}_{2}\)) will move from one cage to another cage, for example, small to small, or small to large, or large to large.