Nonadiabatic transition state theory (NA-TST) is a powerful tool to investigate the nonradiative transitions between electronic states with different spin multiplicities. The statistical nature of NA-TST provides an elegant and computationally inexpensive way to calculate the rate constants for intersystem crossings, spin-forbidden reactions, and spin-crossovers in large complex systems. The relations between the microcanonical and canonical versions of NA-TST and the traditional transition state theory are shown, followed by a review of the basic steps in a typical NA-TST rate constant calculation. These steps include evaluations of the transition probability and coupling between electronic states with different spin multiplicities, a search for the minimum energy crossing point (MECP), and computing the densities of states and partition functions for the reactant and MECP structures. The shortcomings of the spin-diabatic version of NA-TST related to ill-defined state coupling and state counting are highlighted. In three examples, we demonstrate the application of NA-TST to intersystem crossings in the active sites of metal-sulfur proteins focusing on [NiFe]-hydrogenase, rubredoxin, and Fe 2 S 2 -ferredoxin.

1The atomic structure and physical properties of few-layered 111 oriented diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are studied using electronic band structure calculations. It was shown that energy stability linear increases upon increasing of the thickness of proposed structures. All 2D carbon films display direct dielectric band gaps with nonlinear quantum confinement response upon the thickness. Elastic properties of diamanes reveal complex dependence upon increasing of the number of 111 layers. All theoretical results were compared with available experimental data.

Two-layer freestanding heterostructure consisting of VS2 monolayer and graphene was investigated by means of density functional theory computations as a promising anode material for lithium-ion batteries (LIB). We have investigated lithium atoms’ sorption and diffusion on the surface and in the interface layer of VS2/graphene heterostructure with both H and T configurations of VS2 monolayer. The theoretically predicted capacity of VS2/graphene heterostructures is high (569 mAh/g), and the diffusion barriers are considerably lower for the heterostructures than for bulk VS2, so that they are comparable to barriers in graphitic LIB anodes (∼0.2 eV). Our results suggest that VS2/graphene heterostructures can be used as a promising anode material for lithium-ion batteries with high power density and fast charge/discharge rates.

Half-metallic ferromagnetic materials with planar forms are promising for spintronics applications. A wide range of 2D lattices like graphene, h-BN, transition metal dichalcogenides, etc. are non-magnetic or weakly magnetic. Using first principles calculations, the existence of graphene-like hexagonal chromium nitride (h-CrN) with an almost flat atomically thin structure is predicted. We find that freestanding h-CrN has a 100% spin-polarized half-metallic nature with possible ferromagnetic ordering and a high rate of optical transparency. As a possible method for stabilization and synthesis, deposition of h-CrN on 2D MoSe or on MoS is proposed. The formation of composites retains the half-metallic properties and leads to the reduction of spin-down band gaps to 1.43 and 1.71 eV for energetically favorable h-CrN/MoSe and h-CrN/MoS configurations, respectively. Calculation of the dielectric functions of h-CrN, h-CrN/MoSe and h-CrN/MoS exhibit the high transparency of all three low-dimensional nanomaterials. The honeycomb CrN may be considered as a promising fundamental 2D material for a variety of potential applications of critical importance.