Characterizing the local solvation environment of OH(-) in water clusters with AIMD.

In this work, we use ab initio molecular dynamics coupled with metadynamics to explore and characterize the glassy potential energy landscape of the OH(-) in a 20 and 48 water cluster. The structural, energetic, and topological properties of OH(-) are characterized for both clusters and the molecular origins of the IR signatures are examined. We find that in both the small and large clusters, the OH(-) can donate or accept a varying number of hydrogen bonds confirming that the amphiphilic character does not depend on cluster size.

Unveiling the Janus-Like Properties of OH(-).

Using ab initio simulations, we explore the glassy landscape of the OH(-)(H2O)20 cluster and its infrared spectrum. We show that the OH(-) has an amphiphilic Janus-type behavior like the hydronium ion induced by the ability of its O-H bond to be buried inside of the cluster or exposed at the surface with different coordination numbers. Recent infrared experiments of aqueous NaOH have found two pronounced peaks at 2000 and 2850 cm(-1) [Mandal, A.

Collective spin 1 singlet phase in high-pressure oxygen.

Oxygen, one of the most common and important elements in nature, has an exceedingly well-explored phase diagram under pressure, up to and beyond 100 GPa. At low temperatures, the low-pressure antiferromagnetic phases below 8 GPa where O2 molecules have spin S = 1 are followed by the broad apparently nonmagnetic ε phase from about 8 to 96 GPa. In this phase, which is our focus, molecules group structurally together to form quartets while switching, as believed by most, to spin S = 0.

Metadynamics convergence law in a multidimensional system.

Metadynamics is a powerful sampling technique that uses a nonequilibrium history-dependent process to reconstruct the free-energy surface as a function of the relevant collective variables s . In Bussi [Phys. Rev.

Calculating thermodynamics properties of quantum systems by a non-Markovian Monte Carlo procedure.

We present a history-dependent Monte Carlo scheme for the efficient calculation of the free energy of quantum systems inspired by Wang-Landau and metadynamics. In the two-dimensional quantum Ising model, chosen here for illustration, the accuracy of free energy, critical temperature, and specific heat is demonstrated as a function of simulation time and successfully compared with the best available approaches. The approach is based on a path integral formulation of the quantum problem and can be applied without modifications to quantum Hamiltonians of any level of complexity.