N-type AlxGa12xN exhibits a dramatic decrease in the free-carrier concentration for x>0.40. Based on first-principles calculations, we propose that two effects are responsible for this behavior: ~i! in the case of doping with oxygen ~the most common unintentional donor!, a DX transition occurs, which converts the shallow donor into a deep level; and ~ii! compensation by the cation vacancy (VGa ...

A method for the simulation of flows involving a disperse particle phase and a rarefied gas is extended for increased accuracy and efficiency in modeling the high altitude plume flow from a solid propellant rocket. First, a procedure is presented so that calculations involving the interphase transfer of momentum and energy may be avoided in regions where these calculations will have negligible ...

The environment-dependent interaction potential is a transferable empirical potential for carbon which is well suited for studying disordered systems. Ab initio data are used to motivate and parametrize the functional form, which includes environment-dependence in the pair and triple terms, and a generalized aspherical coordination describing dihedral rotation and nonbonded π -repulsion. Simula...

A simple scheme is described for introducing the correct cusps at nuclei into orbitals obtained from Gaussian basis set electronic structure calculations. The scheme is tested with all-electron variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) methods for the Ne atom, the H2 molecule, and 55 molecules from a standard benchmark set. It greatly reduces the variance of ...

An approach is proposed to carry out multivariate calculations of the magnetic field distribution in working gaps a plate polygradient matrix an electromagnetic separator, based on combination advantages two- and three-dimensional computer modeling. Two-dimensional geometric models computational domains are developed, which differ dimensions elements air gaps. To determine vector potential at b...

in this paper,the molecular geometry for three tautomers of uracil and four tautomers of cytosine has been analyzed. vibrational ir spectra of the tautomers were   investigated at hf and b3lyp level using the ab initio 6-31g* and lanl2dz basis sets from the program package gaussian 98 (a.7 public domain version). the physico-chemical and biochemical properties of uracil and cytosine are one of...

maharlu saline lake is located in the sw of iran. to assess the environmental pollution of thelake, the total concentrations of as, cr, co, cu, cd, pb, zn, ni, fe, and mn were determined in the surfacesediments and water of the lake. as and cr were not detected in the water samples, however, the meanconcentrations of other dissolved metals in maharlu lake water were 0.28 mg/l for cu, 0.28 μg/l ...