Nuclear quantum effects influence the structure and dynamics of hydrogen bonded systems, such as water, which impacts their observed properties with widely varying magnitudes. This review highlights the recent significant developments in the experiment, theory and simulation of nuclear quantum effects in water. Novel experimental techniques, such as deep inelastic neutron scattering, now provide a detailed view of the role of nuclear quantum effects in water's 2 properties. These have been combined with theoretical developments such as the introduction of the competing quantum effects principle that allows the subtle interplay of water's quantum effects and their manifestation in experimental observables to be explained. We discuss how this principle has recently been used to explain the apparent dichotomy in water's isotope effects, which can range from very large to almost nonexistent depending on the property and conditions. We then review the latest major developments in simulation algorithms and theory that have enabled the efficient inclusion of nuclear quantum effects in molecular simulations, permitting their combination with on-the-fly evaluation of the potential energy surface using electronic structure theory. Finally, we identify current challenges and future opportunities in the area.3

Progress in the atomic-scale modelling of matter over the past decade has been tremendous. This progress has been brought about by improvements in methods for evaluating interatomic forces that work by either solving the electronic structure problem explicitly, or by computing accurate approximations of the solution and by the development of techniques that use the Born-Oppenheimer (BO) forces to move the atoms on the BO potential energy surface. As a consequence of these developments it is now possible to identify stable or metastable states, to sample configurations consistent with the appropriate thermodynamic ensemble, and to estimate the kinetics of reactions and phase transitions. All too often, however, progress is slowed down by the bottleneck associated with implementing new optimization algorithms and/or sampling techniques into the many existing electronic-structure and empirical-potential codes. To address this problem, we are thus releasing a new version of the i-PI software. This piece of software is an easily extensible framework for implementing advanced atomistic simulation techniques using interatomic potentials and forces calculated by an external driver code. While the original version of the code[1] was developed with a focus on path integral molecular dynamics techniques, this second release of i-PI not only includes several new advanced path integral methods, but also offers other classes of algorithms. In other words, i-PI is moving towards becoming a universal force engine that is both modular and tightly coupled to the driver codes that evaluate the potential energy surface and its derivatives.

Kindlin 2, as a focal adhesion protein, controls integrin activation. However, the association of Kindlin 2 with cancer-related signalling pathways is unknown. Here we identified a new direct interaction between Kindlin 2 and the active b-catenin. Importantly, Kindlin 2 forms a tripartite complex with b-catenin and TCF4. Mechanistically, Kindlin 2 selectively strengthens the occupancy of b-catenin on the Wnt target gene Axin2 and enhances Axin2 gene expression. Functionally, the b-cateninAxin2-Snail cascade is required for Kindlin 2-induced tumour cell invasion. Our data indicate that Kindlin 2 is a new regulator of Wnt signalling, providing a mechanistic insight into the role of Kindlin 2 in cancer progression.

Recent experiments have triggered a debate about the ability of protons to transfer through individual layers of graphene and hexagonal boron nitride (h-BN). However, calculations have shown that the barriers to proton penetration can, at more than 3 eV, be excessively high. Here, on the basis of first principles calculations, we show that the barrier for proton penetration is significantly reduced, to less than 1 eV, upon hydrogenation even in the absence of pinholes in the lattice. Analysis reveals that the barrier is reduced because hydrogenation destabilises the initial state (a deep-lying chemisorption state) and expands the honeycomb lattice through which the protons penetrate. This study offers a rationalization of the fast proton transfer observed in experiments, and highlights the ability of proton transport through single-layer materials in hydrogen rich solutions.

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Exposure to oxygen and light undermines chemical stability of metal halide perovskites, while it surprisingly improves their optical properties. Focusing on CH3NH3PbI3, we demonstrate that material degradation and charge carrier lifetimes depend strongly on the oxidation state of the oxygen species. Nonadiabatic molecular dynamics simulations combined with time-domain density functional theory show that a neutral oxygen molecule has little influence on the perovskite stability, while the superoxide and the peroxide accelerate degradation by breaking Pb–I chemical bonds and enhancing atomic fluctuations. Creating electron and/or hole traps, the neutral oxygen and the superoxide decrease charge carrier lifetimes by over 1 and 2 orders of magnitude, respectively. Importantly, photoinduced reduction of oxygen to the peroxide eliminates trap states and extends carrier lifetimes by more than a factor of 2 because it decreases the nonadiabatic coupling and shortens quantum coherence. The simulations indicate that the superoxide should be strongly avoided, for example, by full reduction to the peroxide because it causes simultaneous degradation of perovskite stability and optical properties. The detailed simulations rationalize the complex interplay between the influence of atmosphere and light on perovskite performance, apply to other solar cell materials exposed to natural elements, and provide valuable insights into design of high-performance solar cells.

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We propose a new quantum transition-state theory for calculating Fermi's golden-rule rates in complex multidimensional systems. This method is able to account for the nuclear quantum effects of delocalization, zero-point energy and tunnelling in an electron-transfer reaction. It is related to instanton theory but can be computed by path-integral sampling and is thus applicable to treat molecular reactions in solution. A constraint functional based on energy conservation is introduced which ensures that the dominant paths contributing to the reaction rate are sampled. We prove that the theory gives exact results for a system of crossed linear potentials and also the correct classical limit for any system. In numerical tests, the new method is also seen to be accurate for anharmonic systems, and even gives good predictions for rates in the Marcus inverted regime.