Using density functional theory, we investigate the equilibrium structure, stability, and electronic properties of nanostructured, hydrogen-terminated diamond fragments. The equilibrium atomic arrangement and electronic structure of these nanostructures turn out to be very similar to bulk diamond. We find that such diamondoids may enter spontaneously into carbon nanotubes. Polymerization inside...

On the basis of the density functional theory, we give a clear definition of the free energy landscape. To show the usefulness of the definition, we construct the free energy landscape for rearrangement of atoms in an FCC crystal of hard spheres. In this description, the cooperatively rearranging region (CRR) is clealy related to the hard spheres involved in the saddle between two adjacent basi...

Far-infrared absorption spectra of small neutral and cationic niobium clusters containing 5 to 9 Nb atoms have been obtained by multiple photon dissociation spectroscopy of their argon complexes. The experimental far-IR spectra are recorded in the 85–600 cm−1 region and cover the range of the structure-specific vibrational fundamentals, i.e., the finger-print range, for these metal clusters. Th...

Using a first-principles approach based on density-functional theory, we find that a large tetragonal strain can be induced in PbTiO3 by application of a negative hydrostatic pressure. The structural parameters and the dielectric and dynamical properties are found to change abruptly near a crossover pressure, displaying a ‘‘kinky’’ behavior suggestive of proximity to a phase transition. Analogo...

The enthalpies of formation of transition metals diborides in various structures have been obtained from density functional theory (DFT) calculations in order to determine the ground state at T = 0 K and p = 0. The evolution of the enthalpies of formation along the 3D, 4D, and 5D series has been correlated to the considered crystal structures. In the whole, the calculated values of the enthalpi...

The spirodienone structure in lignin is a relatively recent discovery, and it has been found to occur in lignin of various plant species at concentrations of ∼3%, which is sufficiently high to be important for better understanding of its properties and reactivity. The cyclic structure, with a β-1 bond, has been proposed to be a precursor for acyclic β-1 linkages in lignin. Previous analytical w...

Density-functional theory (DFT) is based on two pivotal theorems due to Hohenberg and Kohn [1]. The first theorem states that the ground-state density ρ(r) of a system of electrons uniquely determines the Hamiltonian and hence all properties that can be derived from it. Using mathematical language we can say that the total electronic energy of the system is a functional of the electron density,

The structural and mechanical properties of graphene-like honeycomb monolayer structures of MoS2 (g-MoS2) under various large strains are investigated using density functional theory (DFT). g-MoS2 is mechanically stable and can sustain extra large strains: the ultimate strains are 0.24, 0.37, and 0.26 for armchair, zigzag, and biaxial deformation, respectively. The in-plane stiffness is as high...

The accuracy and efficiency of ab initio density functional theory calculations depend critically on the choice of pseudopotential. In this study, the merits of using large-core pseudopotentials for the dissociative chemisorption of oxygen on rhodium are discussed. The results show that these efficient pseudopotentials yield adsorption energies and bond distances of the oxygen atom to rhodium t...

We present a derivation of the stress field for an interacting quantum system within the framework of local density functional theory. The formulation is geometric in nature and exploits the relationship between the strain tensor field and Riemannian metric tensor field. Within this formulation, we demonstrate that the stress field is unique up to a single ambiguous parameter. The ambiguity is ...