The intrinsically nonlinear nature of quantum field theory provides a fundamental complication for lattice calculations, when the physical implications of the subtleties of Fourier theory are taken into account. Even though the fundamental fields are constrained to the first Brillouin zone, Fourier theory tells us that the high-momentum components of products of these fields “bleed into” neighb...

the electronic structure, energy band structure and electronic density of 2 sno ceramic in cubicphase have been investigated using first principle full potential-linearized augmented plane wave (fp-lapw)method within density functional theory (dft). local density approximation (lda) and the generalizedgradient approximation (gga), which are based on exchange- correlation energy optimization wer...

There are several classes of coherent phonons whose generation mechanisms are completely different: impulsive stimulated Raman scattering, Brillouin oscillations, and coherent longitudinal-acoustic-phonon Bragg reflection. All of these are investigated in Si/SiGe superlattices using a picosecond ultrasonics technique at room temperature. Bragg reflection for a single vibrational mode is related...

The spectrum εn has a Brillouin-zone like structure with Ω the width of the first zone, i.e. for any solution |un(t)〉 of quasienergy εn, and any integer m, exp(imΩt)|un(t)〉 is also a solution, with eigenvalue εn + mΩ. The states |un(t)〉 form a Hilbert space of T-periodic functions. The inner product in this space can be defined starting from the standard bra-ket inner product 〈•|•〉 for time-ind...

The intrinsically nonlinear nature of quantum field theory provides a fundamental complication for lattice calculations, when the physical implications of the subtleties of Fourier theory are taken into account. Even though the fundamental fields are constrained to the first Brillouin zone, Fourier theory tells us that the high-momentum components of products of these fields “bleed into” neighb...

We present two developments for the numerical integration of a function over Brillouin zone. First, we introduce nonuniform grid, which refer to as Farey that generalizes regular grids. Second, symmetry-adapted Voronoi tessellation, general technique assign weights points in an arbitrary grid. Combining these developments, propose strategy perform zone and interpolation provides significant com...

In this paper energy bands and Berry curvature of graphene was studied. Desired Hamiltonian regarding the next-nearest neighbors obtained by tight binding model. By using the second quantization approach, the transformation matrix is calculated and the Hamiltonian of system is diagonalized. With this Hamiltonian, the band structure and wave function can be calculated. By using calculated wave f...

Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowes...

Since the discovery of the metallic antiferromagnetic (AF) ground state near superconductivity in iron pnictide superconductors1–3, a central question has been whether magnetism in these materials arises from weakly correlated electrons4,5, as in the case of spin density wave in pure chromium6, requires strong electron correlations7, or can even be described in terms of localized electrons8,9 s...