Oligoacenes C(4n+2)H(2n+4) (n=2,...,6) are studied using a variety of ab initio methods. Density functional theory (DFT) optimized geometries were in good agreement with experiment. Vertical and adiabatic ionization potentials and electron affinities were computed with DFT and it was found that standard exchange-correlation (xc) functionals underestimate ionization potentials in oligoacenes. Po...

A recent extensive study has investigated how various exchange-correlation (XC) functionals treat hydrogen bonds in water hexamers and has shown traditional generalized gradient approximation and hybrid functionals used in density-functional (DF) theory to give the wrong dissociation-energy trend of low-lying isomers and van der Waals (vdW) dispersion forces to give key contributions to the dis...

The (generalised) torsion function u of a domain Ω ⊂ IR is a function which is zero on the boundary of the domain and whose Laplacian is minus one at every point in the interior of the domain. Denote by |Ω| the measure of Ω, xc its centroid. We establish, for convex Ω, 3 2(n+ 1)2 ≤ 1 (n + 1)2 |Ω| ∫ Ω u max Ω u ≤ |Ω|u(xc) ∫ Ω u ≤ |Ω| ∫ Ω u max Ω u ≤ 1 2 (n+ 1)(n+ 2). We generalise this to positi...

We calculate the total and differential decay rates for the semi-inclusive nonleptonic decays B → D s Xq (q = c or u) under the factorization hypothesis. The initial bound state effect is treated using the light-cone expansion and the heavy quark effective theory. We investigate the contribution of the penguin amplitude for the decay mode B → D s Xc and find that it is small but non-negligible....

We investigate the effect of exchange and correlation (xc) in low-density electron bilayers. Along with the direct Coulomb interaction, the effective electron-electron interaction mediated by the exchange of virtual polar optical (PO) phonons is considered. We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its...

A percolation argument and a dilute compressible random field Ising model are used to present a simple model for mixed cyanide crystals. The model reproduces quantitatively several features of the phase diagrams altough some crude approximations are made. In particular critical thresholds xc at which ferroelastic first order transitions disappear, are calculated. Moreover, transitions are found...

We solve the long-standing problem of the large overestimation of the static polarizability of conjugated polymers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation (xc) effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory en...

The study of warm dense matter, widely existing in nature and laboratories, is challenging due to the interplay quantum classical fluctuations. We develop a variational diagrammatic Monte Carlo method determine exchange-correlation kernel $K_{\rm XC}(q;T)$ electron gas for broad range temperature $T$ momentum $q$. observe several interesting physics, including $T$-dependent evolution hump struc...

The Mg-doped CuGeO3 system, Cu1-xMgxGeO3, undergoes a first-order phase transition at a critical concentration xc between an antiferromagnetic (AF) state on dimerized lattice (D-AF, i.e. coexistence of AF and SP order parameters) and an AF Néel state on undistorted uniform lattice (U-AF). Previous magnetic susceptibility measurements showed xc = 0.023 while a recent neutron scattering study rep...

Here I propose to extend, analyze and apply a promising acceleration of the method of Schaefer et al. [Sch]. They focus on recovering the conductance and kinetics of potassium currents at the clamp site. Let us begin, as they do, with the simple case of a straight resting fiber of length ` and radius a with a single noninactivating potassium current. We specify a voltage command V (t) at the cl...