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Simulations of condensed matter systems at the hybrid density functional theory level pose significant computational challenges. The elevated costs arise from the non-local nature of the Hartree–Fock exchange (HFX) in conjunction with the necessity to approach the thermodynamic limit. In this work, we address these issues with the development of a new efficient method for the calculation of HFX in periodic systems, employing k-point sampling. We rely on a local atom-specific resolution-of-the-identity scheme, the use of atom-centered Gaussian type orbitals, and the truncation of the Coulomb interaction to limit computational complexity. Our real-space approach exhibits a scaling that is, at worst, linear with the number of k-points. Issues related to basis set diffuseness are effectively addressed through the auxiliary density matrix method. We report the implementation in the CP2K software package, as well as accuracy and performance benchmarks. This method demonstrates excellent agreement with equivalent Γ-point supercell calculations in terms of relative energies and nuclear gradients. Good strong and weak scaling performances, as well as graphics processing unit (GPU) acceleration, make this implementation a promising candidate for high-performance computing. [ABSTRACT FROM AUTHOR]

The Random-Phase approximation (RPA) provides an appealing framework for semi-local density functional theory. In its Resolution-of-the-Identity (RI) approach, it is a very accurate and more cost-effective method than most other wavefunction-based correlation methods. For widespread applications, efficient implementations of nuclear gradients for structure optimizations and data sampling of machine learning approaches are required. We report a well scaling implementation of RI-RPA nuclear gradients on massively parallel computers. The approach is applied to two polymorphs of the benzene crystal obtaining very good cohesive and relative energies. Different correction and extrapolation schemes are investigated for further improvement of the results and estimations of error bars. [ABSTRACT FROM AUTHOR]

Accurate descriptions of intermolecular interactions are of great importance in simulations of molecular liquids. We present an electronic structure method that combines the accuracy of the Harris functional approach with the computational efficiency of approximately linear-scaling density functional theory (DFT). The non-variational nature of the Harris functional has been addressed by constructing a Lagrangian energy functional, which restores the variational condition by imposing stationarity with respect to the reference density. The associated linear response equations may be treated with linear-scaling efficiency in an atomic orbital based scheme. Key ingredients to describe the structural and dynamical properties of molecular systems are the forces acting on the atoms and the stress tensor. These first-order derivatives of the Harris Lagrangian have been derived and implemented in consistence with the energy correction. The proposed method allows for simulations with accuracies close to the Kohn–Sham DFT reference. Embedded in the CP2K program package, the method is designed to enable ab initio molecular dynamics simulations of molecular solutions for system sizes of several thousand atoms. Available subsystem DFT methods may be used to provide the reference density required for the energy correction at near linear-scaling efficiency. As an example of production applications, we applied the method to molecular dynamics simulations of the binary mixtures cyclohexane-methanol and toluene-methanol, performed within the isobaric-isothermal ensemble, to investigate the hydrogen bonding network in these non-ideal mixtures. [ABSTRACT FROM AUTHOR]

A novel strategy for post-synthesis amine borane functionalization of MOFs under gas-solid phase transformation, utilizing gaseous diborane, is reported. The covalently confined amine borane derivative decorated on the framework backbone is stable when preserved at low temperature, but spontaneously liberates soft chemical hydrogen at room temperature, leading to the development of an unusual borenium type species (-NH=BH2+) ion-paired with a hydroborate anion. Furthermore, the unsaturated amino borane (-NH=BH2) and the μ-iminodiborane (-μ-NHB2H5) were detected as final products. A combination of DFT based molecular dynamics simulations and solid state NMR spectroscopy, utilizing isotopically enriched materials, were undertaken to unequivocally elucidate the mechanistic pathways for H2 liberation. [ABSTRACT FROM AUTHOR]

In this study we have used density functional theory calculations to investigate the stability, structure and catalytic properties of Ni clusters supported on CeO2. We have found Ni clusters to be stabilized with increasing cluster size up to ten atoms both as isolated clusters and adsorbed on CeO2(1 1 1). Analysis of the structural properties showed an opening of the Ni particles when deposited on CeO2(1 1 1) indicating facilitated accessibility for reacting molecules. The reactivity of the functionalized surface has been examined on the example of CO2 adsorption and activation and compared to the one on pristine CeO2(1 1 1) and isolated Ni clusters. Furthermore, the effect of Ni cluster deposition on the formation and characteristics of surface and subsurface oxygen vacancies in CeO2 has been investigated. The oxygen vacancy position is found to significantly affect the stability and electronic structure of the Ni/CeO2 system. [ABSTRACT FROM AUTHOR]

cp2 k has become a versatile open-source tool for the simulation of complex systems on the nanometer scale. It allows for sampling and exploring potential energy surfaces that can be computed using a variety of empirical and first principles models. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern and massively parallel hardware. This review briefly summarizes the main capabilities and illustrates with recent applications the science cp2 k has enabled in the field of atomistic simulation. WIREs Comput Mol Sci 2014, 4:15-25. doi: 10.1002/wcms.1159 The authors have declared no conflicts of interest in relation to this article. For further resources related to this article, please visit the WIREs website. [ABSTRACT FROM AUTHOR]

A highly efficient mechanism for the regeneration of the cisbis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenjum (II) sensitizing dye (N3) by I- in acetonitrile has been identified by using molecular dynamics simulation based on density functional theory. Barrier-free complex formation of the oxidized dye with both I- and I2-, and facile dissociation of I2- and I2- from the reduced dye are key steps in this process. In situ vibrational spectroscopy confirms the reversible binding of I2 to the thiocyanate group. Additionally, simulations of the electrolyte near the interface suggest that acetonitrile is able to cover the (101) surface of anatase with a passivating layer that inhibits direct contact of the redox mediator with the oxide, and that the solvent structure specifically enhances the concentration of I- at a distance which further favors rapid dye regeneration. [ABSTRACT FROM AUTHOR]

The dielectric properties of thehydrogen disordered hexagonalphase (Ih) of water ice have been computed using density functionaltheory (DFT) based Monte Carlo simulations in the isobaric–isothermalensemble. Temperature dependent data yield a fit for the Curie–Weisslaw of the system and hence a prediction of the temperature of thephase transition from the Ih phase to the hydrogen ordered ice XIphase. Direct simulations around the phase transition temperatureconfirm and refine the predicted phase transition temperatures andprovide data for further properties, such as the linear thermal expansioncoefficient. Results have been obtained with both hybrid and semilocaldensity functionals, which yields insight in the performance of theelectronic structure method. In particular, the hybrid functionalyields significantly more realistic dielectric constants than thesemilocal variant, namely ε ≈ 116 as opposed to ε≈ 151 at 273 K (εexperiment= 95). This canbe attributed to the tendency of semilocal functionals to be biasedto configurations with a large dipole moment, and their overestimationof the dipole moments of these configurations. This is also reflectedin the estimates of the Ih/XI transition temperature, which is 70–80and 90–100 K for the hybrid and semilocal functional respectively.DFT based sampling of the millions of configurations necessary forthis work has been enabled by a Tree Monte Carlo algorithm, designedfor massively parallel computers. [ABSTRACT FROM AUTHOR]

Singlet excited state geometries of a set of medium sized molecules with different characteristic lowest excitations are studied. Geometry optimizations of excited states are performed with two closely related restricted open-shell Kohn–Sham methods and within linear response to time-dependent density functional theory. The results are compared to wave-function based methods. Excitation energies (vertical and adiabatic) calculated from the open-shell methods show systematic errors depending on the type of excitation. However, for all states accessible by the restricted methods a good agreement for the geometries with time-dependent density functional theory and wave-function based methods is found. An analysis of the energy with respect to the mixing angle for the singly occupied orbitals reveals that some states (mostly [n→π*]) are stable when symmetry constraints are relaxed and others (mostly [π→π*]) are instable. This has major implications on the applicability of the restricted open-shell methods in molecular dynamics simulations. [Copyright &y& Elsevier]