In 1962, Overhauser showed that within Hartree-Fock (HF) the electron gas is unstable to a spin-density wave state. Determining the true HF ground state has remained a challenge. Using numerical calculations for finite systems and analytic techniques, we study the unrestricted HF ground state of the three-dimensional electron gas. At high density, we find broken spin symmetry states with a near...

In this paper, the hydrogen bonding (HB) effects on the NMR chemical shifts of selected atoms in serineand serine-nH2O complexes (from one to ten water molecules) have been investigated with quantummechanical calculations of the 15N and 13C tensors. Interaction with water molecules causes importantchanges in geometry and electronic structure of serine.For the compound studied, the most importan...

A simple, flexible method of postfabrication positioning of resonance wavelengths of long-period cladding-modecoupled gratings is proposed. This method is based on changing the outer fiber diameter. Reducing the diameter by etching the fiber in HF acid shifts the loss peaks to higher wavelengths. A shift as large as 130 nm after 5 min of HF etching was observed for our strongest grating peak, c...

The projected shell model is used to study the multi-quasiparticle and collective excitations of Hf. With an axially symmetric basis, the spin-16 isomer at 2.4 MeV appears to be well separated in energy/spin space from other configurations. However, projected energy surface calculations suggest that Hf has significant softness to axially asymmetric shapes, which can strongly modify the level di...

We predict ionization potentials of superheavy elements No, Lr, and Rf and their ions using a relativistic hybrid method that combines configuration interaction (CI) with the linearized coupled-cluster approach. Extensive study of the completeness of the four-electron CI calculations for Hf and Rf was carried out. As a test of theoretical accuracy, we also calculated ionization potential of Yb,...

the combination of quantum mechanics (qm) and molecular mechanics (mm) methods hasbecome alternative tool for many applications that pure qm and mm could not be suitable.the qm/mm method has been used for different type of problems, for example: structuralbiology, surface phenomena, and liquid phase. in this paper we have performed these methods forsome antibiotics and vitamins and then we comp...

First principles study of structural, elastic, and electronic properties of the cubic perovskitetype BaHfO3 has been performed using the plane wave ultrasoft pseudo-potential method based on density functional theory with revised Perdew-Burke-Ernzerhof exchange-correlation functional of the generalized gradient approximation (GGA-RPBE). The calculated equilibrium lattice constant of this compou...