A prediction of high temperature magnetic coupling in transition metal phthalocyanines.

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100 K.

Paramagnetic States in Oxygen-Doped Boron Nitride Extend Light Harvesting and Photochemistry to the Deep Visible Region.

A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered.

Mind the Interface Gap: Exposing Hidden Interface Defects at the Epitaxial Heterostructure between CuO and CuO.

Well designed and optimized epitaxial heterostructures lie at the foundation of materials development for photovoltaic, photocatalytic, and photoelectrochemistry applications. Heterostructure materials offer tunable control over charge separation and transport at the same time preventing recombination of photogenerated excitations at the interface. Thus, it is of paramount importance that a detailed understanding is developed as the basis for further optimization strategies and design.

Strain-Tuneable Magnetism and Spintronics of Distorted Monovacancies in Graphene.

The electronic and spintronic properties of the monovacancies in freestanding and isotopically compressed graphene are investigated using hybrid exchange density functional perturbation theory. When the effects of electronic self-interaction are taken into account, an integer magnetic moment of 2 μ is identified for a Jahn-Teller reconstructed V(5-9) monovacancy in freestanding graphene. For graphene with stable ripples induced by a compressive strain of 5%, a bond reconstruction produces a V(55-66) structure for the monovacancy, which is localized at the saddle points of the ripple.

Monomolecular Cracking of Propane: Effect of Zeolite Confinement and Acidity.

The effect of zeolite pore geometry and intrinsic acidity on the activation energy of propane monomolecular cracking was investigated for six topologically distinct zeolites with different pore sizes. Periodic density functional theory calculations were used to calculate the activation energy, while cluster models were used to calculate deprotonation energies. The computed intrinsic activation energies showed a smaller variation with topology than the adsorption energies.

First Principles Calculations on the Stoichiometric and Defective (101) Anatase Surface and Upon Hydrogen and HPc Adsorption: The Influence of Electronic Exchange and Correlation and of Basis Set Approximations.

Anatase TiO provides photoactivity with high chemical stability at a reasonable cost. Different methods have been used to enhance its photocatalytic activity by creating band gap states through the introduction of oxygen vacancies, hydrogen impurities, or the adorption of phthalocyanines, which are usually employed as organic dyes in dye-sensitized solar cells. Predicting how these interactions affect the electronic structure of anatase requires an efficient and robust theory.

Unravelling Some of the Structure-Property Relationships in Graphene Oxide at Low Degree of Oxidation.

Graphene oxide (GO) is a versatile 2D material whose properties can be tuned by changing the type and concentration of oxygen-containing functional groups attached to its surface. However, a detailed knowledge of the dependence of the chemo/physical features of this material on its chemical composition is largely unknown. We combine classical molecular dynamics and density functional theory simulations to predict the structural and electronic properties of GO at low degree of oxidation and suggest a revision of the Lerf-Klinowski model.

A hybrid-exchange density functional study of the bonding and electronic structure in bulk CuFeS2.

The geometric, electronic, and magnetic properties of bulk chalcopyrite CuFeS2 have been investigated using hybrid-exchange density functional theory calculations. The results are compared with available theoretical and experimental data. The theoretical description of the bonding and electronic structure in CuFeS2 is analyzed in detail and compared to those computed for chalcocite (CuS2) and greigite (Fe3S4).

Diffraction of helium on MgO(100) surface calculated from first-principles.

In this work we simulate the diffraction peak intensities of He beams scattered on the MgO(100) surface from first principles. It turns out that diffraction peak intensities are extremely sensitive to the quality of the potential describing the He-MgO surface interaction. Achieving the required accuracy in first principles calculations is very challenging indeed.

Ab initio calculation of the MgO(100) interaction with He and Ne: a HF + MP2 and HF + MP2(B3LYP) comparison.

Second order Rayleigh Schrödinger perturbation theory is applied to calculate the correlation energy contribution to the London dispersion interaction to approximate the interaction of the He and Ne with the MgO(100) surface; single particle orbitals using either Hartree-Fock theory or hybrid-exchange density functional theory are used as the reference state.

An alternative approach for the calculation of correlation energy in periodic systems: a hybrid MP2(B3LYP) study of the He-MgO(100) interaction.

A practical and efficient method for exploiting second order Rayleigh-Schrödinger perturbation theory to approximate the correlation energy contribution to the London dispersion interaction is presented. The correlation energy is estimated as the Møller-Plesset contribution computed using single particle orbitals from hybrid exchange density functional theory as the reference state.

Implementation of the finite field perturbation method in the CRYSTAL program for calculating the dielectric constant of periodic systems.

The finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results.