CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post–Hartree–Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.

Recent advances in the theory of polarization and the development of linear-scaling methods have revitalized interest in the use of Wannier functions for obtaining a localized orbital picture within a periodic supercell. To examine complex chemical systems it is imperative for the localization procedure to be efficient; on the other hand, the method should also be simple and general. Motivated to meet these requirements we derive in this paper a spread functional to be minimized as a starting point for obtaining maximally localized Wannier functions through a unitary transformation. The functional turns out to be equivalent to others discussed in the literature with the difference of being valid in simulation supercells of arbitrary symmetry in the ⌫-point approximation. To minimize the spread an iterative scheme is developed and very efficient optimization methods, such as conjugate gradient, direct inversion in the iterative subspace, and preconditioning are applied to accelerate the convergence. The iterative scheme is quite general and is shown to work also for methods first developed for finite systems ͑e.g., Pipek-Mezey, Boys-Foster͒. The applications discussed range from crystal structures such as Si to isolated complex molecules and are compared to previous investigations on this subject.

Ions and ion pairs are the species that lead to CaCO3 nucleation.

The interplay between crystal and solvent structure, interparticle forces and ensemble particle response dynamics governs the process of crystallization by oriented attachment (OA), yet a quantitative understanding is lacking. Using ZnO as a model system, we combine in situ TEM observations of single particle and ensemble assembly dynamics with simulations of interparticle forces and responses to relate experimentally derived interparticle potentials to the underlying interactions. We show that OA is driven by forces and torques due to a combination of electrostatic ion-solvent correlations and dipolar interactions that act at separations well beyond 5 nm. Importantly, coalignment is achieved before particles reach separations at which strong attractions drive the final jump to contact. The observed barrier to attachment is negligible, while dissipative factors in the quasi-2D confinement of the TEM fluid cell lead to abnormal diffusivities with timescales for rotation much less than for translation, thus enabling OA to dominate.

We exploit gas-phase cluster ion techniques to provide insight into the local interactions underlying divalent metal ion-driven changes in the spectra of carboxylic acids at the air–water interface. This information clarifies the experimental findings that the CO stretching bands of long-chain acids appear at very similar energies when the head group is deprotonated by high subphase pH or exposed to relatively high concentrations of Ca2+ metal ions. To this end, we report the evolution of the vibrational spectra of size-selected [Ca2+·RCO2−]+·(H2O)n=0to12 and RCO2−·(H2O)n=0to14 cluster ions toward the features observed at the air–water interface. Surprisingly, not only does stepwise hydration of the RCO2− anion and the [Ca2+·RCO2−]+ contact ion pair yield solvatochromic responses in opposite directions, but in both cases, the responses of the 2 (symmetric and asymmetric stretching) CO bands to hydration are opposite to each other. The result is that both CO bands evolve toward their interfacial asymptotes from opposite directions. Simulations of the [Ca2+·RCO2−]+·(H2O)n clusters indicate that the metal ion remains directly bound to the head group in a contact ion pair motif as the asymmetric CO stretch converges at the interfacial value by n = 12. This establishes that direct metal complexation or deprotonation can account for the interfacial behavior. We discuss these effects in the context of a model that invokes the water network-dependent local electric field along the C–C bond that connects the head group to the hydrocarbon tail as the key microscopic parameter that is correlated with the observed trends.

The ability to reproduce the experimental structure of water around the sodium and potassium ions is a key test of the quality of interaction potentials due to the central importance of these ions in a wide range of important phenomena.

The nonequilibrium molecular dynamics generated by the SLLOD algorithm [so called due to its association with the DOLLS tensor algorithm (D. J. Evans and G. P. Morriss, Statistical Mechanics of Nonequilibrium Liquids (Academic, New York, 1990)] for fluid flow is considered. It is shown that, in the absence of time-dependent boundary conditions (e.g., shearing boundary conditions via explicit cell dynamics or Lees–Edwards boundary conditions), a conserved energy, H exists for the equations of motion. The phase space distribution generated by SLLOD dynamics can be explicitly derived from H. In the case of a fluid confined between two immobile boundaries undergoing planar Couette flow, the phase space distribution predicts a linear velocity profile, a fact which suggests the flow is field driven rather than boundary driven. For a general flow in the absence of time-dependent boundaries, it is shown that the SLLOD equations are no longer canonical in the laboratory momenta, and a modified form of the SLLOD dynamics is presented which is valid arbitrarily far from equilibrium for boundary conditions appropriate to the flow. From an analysis of the conserved energy for the new SLLOD equations in the absence of time-dependent boundary conditions, it is shown that the correct local thermodynamics is obtained. In addition, the idea of coupling each degree of freedom in the system to a Nosé–Hoover chain thermostat is presented as a means of efficiently generating the phase space distribution.

Although interfacial solution structure impacts environmental, biological, and technological phenomena, including colloidal stability, protein assembly, heterogeneous nucleation, and water desalination, its molecular details remain poorly understood. Here, we visualize the three-dimensional (3D) hydration structure at the boehmite(010)−water interface using fast force mapping (FFM). Using a self-consistent scheme to decouple long-range tip-sample interactions from short-range solvation forces, we obtain the solution structure with lattice resolution. The results are benchmarked against molecular dynamics simulations that explicitly include the effects of the tip with different levels of approximation and systematically account for tip size, chemistry, and confinement effects. We find four laterally structured water layers within 1 nm of the surface, with the highest water densities at sites adjacent to hydroxyl groups. The key features beyond the first two layers can only be predicted using a full-scale simulation of the boehmite−water−silica system. Our findings further reveal a complex relationship between site-specific chemistry, water density, and long-range particle interactions; and present important advances toward quantitative data interpretation in 3D FFM.