نشریه پژوهش سیستم های بس ذره ای
سال سوم شماره 2 (پیاپی 6، زمستان 1392)

We have used a many-body method based on the cluster expansion of the energy to calculate the free energy، entropy، equation of state، heat capacity and incompressibility of the two dimensional liquid helium-3. In these calculations، we have used the Lennard-Jones potential as the inter atomic interaction. Our calculations show that the free energy increases by increasing the density، and decreases by increasing temperature. We have also shown that the two dimensional liquid helium-3 has no bond state. Our results indicate that the equation of state of the system becomes stiffer as the temperature increases. For heat capacity، it was seen that reaches the limiting value 1 k_B at high temperatures. This means that our system has a behavior the same as two dimensional classical ideal gas. Also، our results have shown that as the density and temperature increase، the system becomes more incompressible.

Electronic and optical properties of Cu2-II-IV-VI4 (II=Zn،Cd; IV=Ge،Sn; VI=S،Se،Te) quaternary chalcogenides are calculated using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) and the calculated results are compared with the available experimental results. The real and imaginary parts of the dielecteric function ԑ (ω)، the electron energy loss function (EELS) and the optical absorption coefficient I (ω) are calculated within the random phase approximation (RPA). The prominent structures in the specrta of ԑ1 (ω)، ԑ2 (ω) and EELS are discussed in detail and the static dielectric constants of these compounds are calculated. The most prominent feature of these compounds is their high absorption coefficient and wide absorption spectrum. It is an appropriate parameter for using in solar cells. The band structures are calculated using Perdew et al.، Engel-Vosko and modified Becke-Johnson schemes and the effect of the exchange-correlation functional on the band gap of these compounds is investigated. It is shown that mBJ-GGA leads to a better result.

In this paper، we study the NdMnO3 manganite compound based on the density function theory and using the local spin density LSDA and local spin density plus Hubbard energy LSDA+U approximations. The magnetic and electronic structures of this system were studied using these approximations. After the optimization of volume and structure parameters، the ground state magnetic phase، magnetic moments of atoms and local and total density of states of the atoms were calculated by considering different Hubbard energy. The results of ground state energy showed that although the ferromagnetic and anti-ferromagnetic phases are in competition but the ferromagnetic phase is more stable. The magnetic moments and the density of states calculated from LSDA+U lead to reasonable result but LSDA results are not accurate. The results of density of states indicated that the 3d orbitals of Mn atom، contributed in conduction and hybridization، are the most effective orbital in magnetic properties of the compound.

In this paper، we have considered the energy spectra and quadruple transition probabilities of even-even Er isotopes via partial dynamical symmetry in interacting boson model framework. The advantage of using interactions with a partial dynamical symmetry is that they can be introduced، in a controlled manner، without destroying results previously obtained with a dynamical symmetry for a segment of the spectrum. Partial dynamical SU (3) symmetry has an accurate description for nuclei which exhibit rotational deformed structure because of removing undesired degeneracies from energy spectrum of them. The agreement with the most recent experimental counterparts is acceptable. Also، there are some suggestions about the reduction of uncertainty with increasing the neutron number and quadrupole deformation parameter.

In this paper، the frustrated dimerized antiferromagnetic isotropic s=1/2 Heisenberg chain is studied. In this model، denotes the dimerization parameter for the exchange of nearest neighbors and denotes the frustration parameter for the exchange of next nearest neighbor interaction. Using the numerical Lanczos method، we have studied the magnetic phase diagram of the model in two subspaces. We have calculated the response functions of the system as a function of the frustrated parameter. According to the exact diagonalization results، by calculating order parameter، it is argued that، adding the dimerization will cause a phase transition between two different types of dimer phases.

In this paper، the electronic، phononic and mechanical properties of zinc-blende and wurtzite phases of GaN compound are studied by Density Functional Theory (DFT)، generalized gradient approximation (GGA) and pseudo potentials. Results show both phases are semiconductors. The calculated band gaps are 2 and 2. 2 eV for zinc-blende and wurtzite phases correspondingly. Bulk modules are obtained by fitting the variation of energy vs. the lattice constants data to the murnaghan equation of state. The phonon dispersion curves are obtained in high symmetry directions. The elastic constants are calculated by the slope of the phonon acoustic modes in different directions. These constants are =272، =122 and =127 GPa in zinc-blende phase and =301، =380، =85، =88، =125، =153 GPa in wurtzite phase. Our results are compared with other calculation and are in good agreement with them. Young modules are calculated in tensile and comparison modes for wurtzite phase and compared with zinc-blende phase. The results show; the wurtzite phase is harder in z direction.