Pt3 and Pt4 clusters on graphene monolayers supported on a Ni(111) substrate: relativistic density-functional calculations.

Density-functional theory including spin-orbit coupling and corrections for dispersion forces has been used to investigate the structural and magnetic properties of Pt(3) and Pt(4) clusters deposited on a graphene layer supported on a Ni(111) substrate. It is shown that the strong interaction of the Pt atoms with the Ni-supported graphene stabilizes a flat triangular and a slightly bent rhombic structure of the clusters. Pt atoms are located nearly on top of the C atoms of the graphene layer, slightly shifted towards the bridge positions because the Pt-Pt distances are larger than the C-C distances of the graphene sheet lattice-matched to the Ni support.

Pt on graphene monolayers supported on a Ni(111) substrate: relativistic density-functional calculations.

The structural, energetic, and magnetic properties of Pt atoms and dimers adsorbed on a Ni-supported graphene layer have been investigated using density-functional calculations, including the influence of dispersion forces and of spin-orbit coupling. Dispersion forces are found to be essential to stabilize a chemisorbed graphene layer on the Ni(111) surface. The presence of the Ni-substrate leads not only to a stronger interaction of Pt atoms and dimers with graphene but also to a locally increased binding between graphene and the substrate and a complex reconstruction of the adlayer.

Tailor-made ultrathin manganese oxide nanostripes: 'magic widths' on Pd(1 1 N) terraces.

The growth of ultrathin two-dimensional manganese oxide nanostripes on vicinal Pd(1 1 N) surfaces leads to particular stable configurations for certain combinations of oxide stripe and substrate terrace widths. Scanning tunneling microscopy and high-resolution low-energy electron diffraction measurements reveal highly ordered nanostructured surfaces with excellent local and long-range order. Density functional theory calculations provide the physical origin of the stabilization mechanism of 'magic width' stripes in terms of a finite-size effect, caused by the significant relaxations observed at the stripe boundaries.

Natural Orbitals for Wave Function Based Correlated Calculations Using a Plane Wave Basis Set.

We demonstrate that natural orbitals allow for reducing the computational cost of wave function based correlated calculations, especially for atoms and molecules in a large box, when a plane wave basis set under periodic boundary conditions is used. The employed natural orbitals are evaluated on the level of second-order Møller-Plesset perturbation theory (MP2), which requires a computational effort that scales as [Formula: see text](N(5)), where N is a measure of the system size. Moreover, we find that a simple approximation reducing the scaling to [Formula: see text](N(4)) yields orbitals that allow for a similar reduction of the number of virtual orbitals.

Geometric and magnetic properties of Pt clusters supported on graphene: relativistic density-functional calculations.

The geometric and magnetic structures of small Pt(n) clusters (n = 1 - 5) supported on a graphene layer have been investigated using ab initio density functional calculations including spin-orbit coupling. Pt-Pt interactions were found to be much stronger than the Pt-C interactions promoting the binding to the support. As a consequence, the equilibrium structure of the gas-phase clusters is preserved if they are deposited on graphene.

Thickness dependent structural and electronic properties of CuO grown on SrTiO₃(100): a hybrid density functional theory study.

We discuss the structural and electronic properties of tetragonal CuO grown on SrTiO₃(100) by means of hybrid density functional theory. Our analysis explains the anomalously large Cu-O vertical distance observed in the experiments (≈2.7 Å) in terms of a peculiar frustration between two competing local Cu-O environments characterized by different in-plane and out-of-plane bond lengths and Cu electronic populations.

Second-order Møller-Plesset perturbation theory applied to extended systems. II. Structural and energetic properties.

Results for the lattice constants, atomization energies, and band gaps of typical semiconductors and insulators are presented for Hartree-Fock and second-order Moller-Plesset perturbation theory (MP2). We find that MP2 tends to undercorrelate weakly polarizable systems and overcorrelates strongly polarizable systems. As a result, lattice constants are overestimated for large gap systems and underestimated for small gap systems.

Making the random phase approximation to electronic correlation accurate.

We show that the inclusion of second-order screened exchange to the random phase approximation allows for an accurate description of electronic correlation in atoms and solids clearly surpassing the random phase approximation, but not yet approaching chemical accuracy. From a fundamental point of view, the method is self-correlation free for one-electron systems. From a practical point of view, the approach yields correlation energies for atoms, as well as for the jellium electron gas within a few kcal/mol of exact values, atomization energies within typically 2-3 kcal/mol of experiment, and excellent lattice constants for ionic and covalently bonded solids (0.

Kinetic Monte Carlo simulations of temperature programed desorption of O/Rh(111).

We present a kinetic Monte Carlo simulation based on ab initio calculations for the thermal desorption of oxygen from a Rh(111) surface. Several models have been used for the parametrization of the interaction between the adsorbed atoms. We find that models based on a parametrization with only pairwise interactions have a relatively large error in the predicted adsorption energies.

Orientational dynamics and dielectric response of nanopore water.

We present numerical calculations, simulation results, and analytical considerations for the frequency-dependent dielectric constant of single-file water in narrow nanopores, described by a recently developed dipole lattice model. We find Debye relaxation over all length scales with relaxation times that strongly depend on pore length. This behavior is analyzed in terms of the dynamics of orientational defects leading to simple quantitative expressions for the static dielectric susceptibility and the relaxation time in the limits of short and long pores.

Second-order Møller-Plesset perturbation theory applied to extended systems. I. Within the projector-augmented-wave formalism using a plane wave basis set.

We present an implementation of the canonical formulation of second-order Møller-Plesset (MP2) perturbation theory within the projector-augmented-wave method under periodic boundary conditions using a plane wave basis set. To demonstrate the accuracy of our approach we show that our result for the atomization energy of a LiH molecule at the Hartree-Fock+MP2 level is in excellent agreement with well converged Gaussian-type-orbital calculations. To establish the feasibility of employing MP2 perturbation theory in its canonical form to systems that are periodic in three dimensions we calculated the cohesive energy of bulk LiH.

Nucleation and growth in structural transformations of nanocrystals.

Using transition path sampling computer simulations, we reveal the nucleation mechanism of a pressure-induced structural transformation in CdSe nanocrystals. Consistent with experiments, the thermodynamic transition pressure of the transformation increases with decreasing crystal size. Through transition state analysis, we identify the critical nuclei and characterize them by calculating activation enthalpies and volumes.

Precision shooting: Sampling long transition pathways.

The kinetics of collective rearrangements in solution, such as protein folding and nanocrystal phase transitions, often involve free energy barriers that are both long and rough. Applying methods of transition path sampling to harvest simulated trajectories that exemplify such processes is typically made difficult by a very low acceptance rate for newly generated trajectories. We address this problem by introducing a new generation algorithm based on the linear short time behavior of small disturbances in phase space.

Ab-initio simulations of materials using VASP: Density-functional theory and beyond.

During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science-promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures.

Single molecule pulling with large time steps.

Recently, we presented a generalization of the Jarzynski nonequilibrium work theorem for phase space mappings. The formalism shows that one can determine free energy differences from approximate trajectories obtained from molecular dynamics simulations in which very large time steps are used. In this work we test the method by simulating the force-induced unfolding of a deca-alanine helix in vacuum.

Mechanisms of the wurtzite to rocksalt transformation in CdSe nanocrystals.

We study the pressure-driven phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure in CdSe nanocrystals with molecular dynamics computer simulations. With an ideal gas as the pressure medium, we apply hydrostatic pressure to spherical and faceted nanocrystals ranging in diameter from 25 to 62 A. In spherical crystals, the main mechanism of the transformation involves the sliding of (100) planes, but depending on the specific surface structure we also observe a second mechanism proceeding through the flattening of (100) planes.