Lattice instability and martensitic transformation in LaAg predicted from first-principles theory

The electronic structure, elastic constants and lattice dynamics of the B(2) type intermetallic compound LaAg are studied by means of density functional theory calculations with the generalized gradient approximation for exchange and correlation. The calculated equilibrium properties and elastic constants agree well with available experimental data. From the ratio between the bulk and shear moduli, LaAg is found to be ductile, which is unusual for B(2) type intermetallics. The computed band structure shows a dominant contribution from La 5d states near the Fermi level. The phonon dispersion relations, calculated using density functional perturbation theory, are in good agreement with available inelastic neutron scattering data. Under pressure, the phonon dispersions develop imaginary frequencies, starting at around 2.3 GPa, in good accordance with the martensitic instability observed above 3.4 GPa. By structural optimization the high pressure phase is identified as orthorhombic B(19).     

Test of the Skyrme effective field theory using quenched lattice QCD

The Skyrme effective field theory is tested by evaluating nucleon ground-state matrix elements of the correlation functions for two flavor density operators and two pseudoscalar density operators in the Skyrme model and comparing them with results in quenched lattice QCD. The possibility of using quenched lattice QCD to study higher-order terms in effective field theory is also discussed.     

Wetting, drying, and layering of colloid-polymer mixtures at porous interfaces

The influence of interface porosity on the wetting properties of colloid-polymer mixtures is studied within density functional theory for the Asakura-Oosawa-Vrij model at the surface of a quenched hard-sphere matrix. While the porosity hardly changes the location of the transition from partial to complete wetting at colloidal bulk gas-liquid coexistence, the onset of wetting, as signaled by the first discontinuous layering transition, can be efficiently controlled by tailoring the porosity. We furthermore find that the penetrability of the porous interface induces complete drying into the matrix upon approaching capillary coexistence.     

Adsorption isotherm of a Lennard-Jones nitrogen in a carbon slitlike pore

A density functional perturbation approximation based both on second-order perturbation theory and on the pore average density has been proposed to study the adsorption hysteresis of nitrogen in a carbon slit pore. The main advantage of the present approximation is that it is computationally much simpler than the original density functional approximation based on the second-order perturbation theory of liquids, and can be applied to several model fluids confined in a strong external field in order to study their structural and thermodynamic properties. The calculated adsorption hysteresis for the confined Lennard-Jones nitrogen is in very good agreement with computer simulation, even if its accuracy slightly deteriorates for the desorption branch. The calculated equilibrium particle density distributions also compare well with computer simulations, and are better than those of a density functional theory based on the so-called mean-field approximation.     

Density functional. Theory and application to atoms and molecules

The density functional theory is one of the most efficient and promising methods of quantum physics and chemistry. It is a theory of electronic structure formulated in terms of the electron density as the basic unknown function instead of the electron wave function. According to the fundamental theorems of Hohenberg and Kohn, the electron density carries all the information one might need to determine any property of the electron system. However, the way of obtaining it, is not at all trivial. In this report, the recent advances are summarized. After a review of the Hohenberg–Kohn theorems, the method of constrained search and the Kohn–Sham scheme, exact theorems, relations and inequalities are discussed. There are several important concepts of chemistry (e.g. electronegativity, hardness, softness) that have recently obtained a firm foundation in the density functional theory. The optimized potential method and the methods that generate the potential from the electron density are reviewed. The local and nonlocal approximate functionals are compared. Extensions of the ground-state density functional theory (excited states, time-dependent, relativistic and finite temperature) are summarized. A review of the applications to atoms and molecules is presented.     

Aspects of the functional renormalisation group

We discuss structural aspects of the functional renormalisation group. Flows for a general class of correlation functions are derived, and it is shown how symmetry relations of the underlying theory are lifted to the regularised theory. A simple equation for the flow of these relations is provided. The setting includes general flows in the presence of composite operators and their relation to standard flows, an important example being NPI quantities. We discuss optimisation and derive a functional optimisation criterion. Applications deal with the interrelation between functional flows and the quantum equations of motion, general Dyson-Schwinger equations. We discuss the combined use of these functional equations as well as outlining the construction of practical renormalisation schemes, also valid in the presence of composite operators. Furthermore, the formalism is used to derive various representations of modified symmetry relations in gauge theories, as well as to discuss gauge-invariant flows. We close with the construction and analysis of truncation schemes in view of practical optimisation.     

Investigating the topological structure of quenched lattice QCD with overlap fermions using a multi-probing approximation

The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent.Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 16~3×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion.     

Quenching of the magnetic moment of a transition metal dopant in silver clusters

Single magnetic atoms embedded in a nonmagnetic host exhibit the Kondo effect in the bulk limit, while in very small molecules the magnetic atom is hardly affected by the matrix. In a combined theoretical (density functional theory) and experimental (photofragmentation and mass spectrometry) study we consider the intermediate case of nanometer sized transition-metal-doped silver clusters. In particular, we provide experimental evidence for enhanced stability of the cobalt-doped silver cluster Ag10Co+ and show theoretically that it has a symmetric endohedral geometry with a closed 18-electron singlet electronic shell structure. This implies that the magnetic moment on the cobalt atom is quenched.     

Quenched Kosterlitz-Thouless superfluid transitions

Rapidly quenched Kosterlitz-Thouless (KT) superfluid transitions are studied by solving the Fokker-Planck equation for the vortex-pair dynamics in conjunction with the KT recursion relations. Power-law decays of the vortex density at long times are found, and the results are in agreement with a scaling proposal made by Minnhagen and co-workers for the dynamical critical exponent. The superfluid density is strongly depressed after a quench, with the subsequent recovery being logarithmically slow for starting temperatures near T(KT). No evidence is found of vortices being "created" in a rapid quench; there is only decay of the existing thermal vortex pairs.     

Ab initio study of structural,electronic and dynamical properties of MgAuSn

The structural and electronic properties of MgAuSn in the cubic AlLiSi structure have been studied, using density functional theory within the local density approximation. The calculated lattice constant for MgAuSn is found to be in good agreement with its experimental value. Our calculated electronic structure is also compared in detail with a recent tight-binding. A linear-response approach to density-functional theory is used to calculate the phonon spectrum and density of states for MgAuSn.     

Structure-property relations and thermodynamic properties of monoclinic petalite, LiAlSi(4)O(10)

Structure-property relations of monoclinic petalite, LiAlSi(4)O(10), were determined by experiment and atomistic modeling based on density functional theory. The elastic stiffness coefficients were measured between room temperature and 570?K using a combination of the plate-resonance technique and resonant ultrasound spectroscopy. The thermal expansion was studied between 100 and 740?K by means of dilatometry. The heat capacity between 2 and 398?K has been obtained by microcalorimetry using a quasi-adiabatic calorimeter. The experimentally determined elastic stiffness coefficients were employed to benchmark the results of density functional theory based model calculations. The values in the two data sets agreed to within a few GPa and the anisotropy was very well reproduced. The atomistic model was then employed to predict electric field gradients, the lattice dynamics and thermodynamic properties. The theoretical charge density was analyzed to investigate the bonding between atoms.     

Christopher Longuet-Higgins, 1923 to 2004

The structure, harmonic vibrational frequencies, dissociation energies with respect to possible fragmentation pathways, dipole moment, natural bond orbital (NBO) partial atomic charges and time-dependent density functional theory (TD-DFT) excitation energies for the novel molecule periodane, FBeCNLiOB, and three structural analogues were computed using density functional theory (DFT). Two isoelectronic analogues (FBeCNLiNC and FBeBOLiOB) result from the replacement in periodane of the BO fragment with the CN fragment and vice versa, while the third, called hydroperiodane, is formed by replacing the F atom of periodane with a H atom. These three species are predicted to have a stable structural motif based on that of the theoretically predicted planar global minimum of the periodane molecule.     

Theoretical examination of electron–phonon interaction and superconductivity in the hexagonal pnictide SrPtAs

We have calculated the structural and electronic properties of SrPtAs in a hexagonal KZnAs-type of crystal structure using a generalized gradient approximation of the density functional theory and the ab initio planewave pseudopotential method. These results are used to further calculate the phonon dispersions curves and the phonon density of states using a linear response approach based on the density functional theory. Using the electronic and phonon results, the electron–phonon coupling is computed to be of the intermediate strength of 0.78. In large part, this is contributed by the phonon modes dominated by the vibrations of Pt and As atoms. The superconducting critical temperature is estimated to be 1.9 K, in good accord with its experimental value of 2.4 K.     

Phonon dispersion relations and soft modes of 4 carbon nanotubes

The phonon dispersion relations of three kinds of 4 carbon nanotubes are calculated by using the density functional perturbation theory. It is found that the frequencies of some phonon modes are very sensitive to the smearing width used in the calculations, and eventually become negative at low electronic temperature. Moreover, two kinds of soft modes are identified for the (5,0) tube which are quite different from those reported previously. Our results suggest that the (5,0) tube remains metallic at very low temperature, instead of the metallic-semiconducting transition claimed before.     

Generalized hydrodynamic equations and correlation functions for thermoviscoelastic fluids

For very viscous liquids a phenomenological theory of thermoviscoelasticity is formulated, in which the retarded reaction of thermal variables, which arises from structural relaxation, is taken into account. The theory describes the effect of the slowing down of the structural relaxation near a glass transition on the fluctuation spectra of density and entropy; in particular, the intensity of the slow relaxational component of the fluctuation spectra, which is frozen in the glass below the glass transition, is derived. Conditions for positive energy dissipation and symmetry relations are obtained in the framework of thermodynamic relaxation theory, and the memory functions occurring in the Mori-Zwanzig projection operator formalism are calculated.Dedicated to K. Dransfeld on the occasion of his 60th birthday     

不同溶剂中硝基苯胺分子非线性光学性质的研究

在含时密度泛函理论水平上研究了溶剂对硝基苯胺分子非线性光学性质的影响 .溶剂效应通过极化连续模型来研究 .首先采用极化连续模型在密度泛函理论水平上优化了硝基苯胺分子在溶剂中的几何结构 ,从而研究了溶剂引起硝基苯胺分子几何结构的变化 .然后采用极化连续模型在含时密度泛函理论水平上计算了不同溶剂中硝基苯胺分子的激发态能量和电偶极矩 ,并利用两态模型首次给出了不同溶剂中二次谐波振荡过程的一阶非线性超极化率的色散关系 .计算结果表明 ,极性溶剂对硝基苯胺分子的非线性光学性质有较大的影响 .在低的辐射场频率下 ,理论给出的一阶非线性超极化率的色散关系和实验结果符合得较好 .最后对所得结果从理论上给出了可能的解释并讨论了两态模型的可靠性 .     

A stochastic theory for clustering of quenched-in vacancies—IV. Continuum model applied to the formation of stacking fault tetrahedra and vacancy loops

The continuum model for the growth of clusters developed in the previous paper (paper III) is applied to the formation of stacking fault tetrahedra in quenched gold and the formation of faulted vacancy loops in quenched aluminium. The results of the theory namely the distribution of the clusters as a function of their size and time, and the average size and the total density of the clusters as a function of time and the ageing temperature are shown to be in good agreement with the experimental results.     

Lattice dynamics properties of zinc-blende and Nickel arsenide phases of AlP

Ab initio calculations, based on norm-conserving non-local pseudopotentials and the density functional theory (DFT), have been performed to investigate the behaviour under hydrostatic pressure of the structural, electronic, elastic and dynamical properties of AlP, in both zinc-blende and nickel arsenide phases. Our calculated structural and electronic properties are in good agreement with previous theoretical and experimental results. The phonon dispersion curves, the elastic constants, Born effective charge, etc., were calculated with the local density approximation and the density functional perturbation theory (DFPT). Our results in the pressure behaviour of the elastic and dynamical properties of both phases are in agreement with the experimental data when available, in other case they can be considered as predictions.