We report the calculations of dielectric functions and quasiparticle lifetimes for noble metals Cu, Ag, and Au performed within the LMTO-GW approach. We show that by changing the value of continuous principal quantum number of d states it is possible to improve the calculated local density approximation ͑LDA͒ band structures and dielectric functions. In particular, the plasmon absorption in Ag, which is absent in the selfconsistent LDA approach, is obtained with the corrected band structure. We also show that the drawbacks of the LDA band structures do not lead to qualitative changes of the quasiparticle lifetimes. The lifetimes of electron excitations calculated by the LMTO-GW method agree well with the results of the LDA plane-wave GW approach. By adjusting the value of the density parameter r s good agreement with the results of the many-body free-electron gas calculations is also achieved for the electrons and holes in s,p-bands. For the holes in the top d bands we report the lifetime band structures.

We report a study of the electronic dissociation energy of the water dimer using quantum Monte Carlo techniques. We have performed variational quantum Monte Carlo and diffusion quantum Monte Carlo (DMC) calculations of the electronic ground state of the water monomer and dimer using all-electron and pseudopotential approaches. We have used Slater-Jastrow trial wave functions with B3LYP type single-particle orbitals, into which we have incorporated backflow correlations. When backflow correlations are introduced, the total energy of the water monomer decreases by about 4-5 mhartree, yielding a DMC energy of -76.428 30(5) hartree, which is only 10 mhartree above the experimental value. In our pseudopotential DMC calculations, we have compared the total energies of the water monomer and dimer obtained using the locality approximation with those from the variational scheme recently proposed by Casula [Phys. Rev. B 74, 161102(R) (2006)]. The time step errors in the Casula scheme are larger, and the extrapolation of the energy to zero time step always lies above the result obtained with the locality approximation. However, the errors cancel when energy differences are taken, yielding electronic dissociation energies within error bars of each other. The dissociation energies obtained in our various all-electron and pseudopotential calculations range between 5.03(7) and 5.47(9) kcalmol and are in good agreement with experiment. Our calculations give monomer dipole moments which range between 1.897(2) and 1.909(4) D and dimer dipole moments which range between 2.628(6) and 2.672(5) D.

We report a study of the structural, vibrational, and electronic properties of layered monoclinic arsenic telluride (α-As 2 Te 3 ) at high pressures. Powder x-ray diffraction and Raman scattering measurements up to 17 GPa have been complemented with ab initio total-energy, lattice dynamics, and electronic band structure calculations. Our measurements, which include previously unreported Raman scattering measurements for crystalline α-As 2 Te 3 , show that this compound undergoes a reversible phase transition above 14 GPa at room temperature. The monoclinic crystalline structure of α-As 2 Te 3 and its behavior under compression are analysed by means of the compressibility tensor. Major structural and vibrational changes are observed in the range between 2 and 4 GPa and can be ascribed to the strengthening of interlayer bonds. No evidence of any isostructural phase transition has been observed in α-As 2 Te 3 . A comparison with other group-15 sesquichalcogenides allows understanding the structure of α-As 2 Te 3 and its behavior under compression based on the activity of the cation lone electron pair in these compounds. Finally, our electronic band structure calculations show that α-As 2 Te 3 is a semiconductor at 1 atm, which undergoes a trivial semiconducting-metal transition above 4 GPa.The absence of a pressure-induced electronic topological transition in α-As 2 Te 3 is discussed.

We report extensive all-electron time-dependent density-functional calculations and nonresonant inelastic x-ray scattering measurements of the dynamical structure factor of 3d transition metals. For small wave vectors, a plasmon peak is observed which is well described by our calculations. At large wave vectors, both theory and experiment exhibit characteristic low-energy electron-hole excitations of d character which correlate with the presence of d bands below and above the Fermi level. Our calculations, which have been carried out in the random-phase and adiabatic local-density approximations, are found to be in remarkable agreement with the measured dynamical structure factor of Sc and Cr at energies below the semicore onset energy (M-edge) of these materials.