Volume variation of nuclear gruneisen parameter for equation of state studies

The method of first principle pseudopotential is used to simulate the volume variation of nuclear Gruneisen parameter. The elements Al and Be, for which Neal's experimental data exist are investigated. The nuclear Gruneisen obtained from the details of phonon frequencies are in better agreement with the experimental data as compared to those obtained from approximate Slater and Dugdale-MacDonald methods, often used in shock wave studies

Electronic structure of MgB<SUB>2</SUB>

Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, c/a ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated D (E F) and the experimental specific heat data. The T c is found to be 24.7 K

On the stability of rhenium up to 1 TPa pressure against transition to the bcc structure

We have carried out electronic structure total energy calculations on rhenium in the hexagonal close packed (hcp) and body centred cubic (bcc) phases, by the full potential linear muffin-tin orbital method, in order to verify the stability of the ambient pressure hep phase against transition to the bcc structure at high pressures. As per our results, no hcp to bcc structural transition can occur up to 1 TPa pressures. Moreover, our Bain path calculations show that face centred cubic and body centred tetragonal structures are also not energetically preferred over hcp in this pressure range. The axial ratio (c/a) of Re changes by less than 0-33% in the pressure range studied

Band theory analysis of shock velocity-particle velocity relations for metals

The systematics of the shock constants in shock velocity-particle velocity relations for metals have been examined by energy band theory methods. The causes of non-linearity of this relation at high pressure are discussed in terms of s ⇌d electron transfer

High pressure studies on YNi<SUB>2</SUB>B<SUB>2</SUB>C and LuNi<SUB>2</SUB>B<SUB>2</SUB>C: ADXRD, thermoelectric power, resistivity, and electronic structure

The electronic and structural behaviour of YNi2B2C and LuNi2B2C at high pressures were investigated by electrical resistivity, thermoelectric power (TEP), and angle dispersive X-ray diffraction measurements and by electronic band structure calculations. The pressure variation of TEP shows a peak around 2 GPa in YNi2B2C. However, the X-ray powder diffraction does not show any structural transition up to 16.4 GPa. The equation of state of YNi2B2C yielded a relatively high bulk modulus of 200 GPa. The observed peak in TEP and the pressure variation of the superconducting transition temperature can be correlated with different components of the electronic density of states. The universal equation of state shows deviation from linearity around 1.5 GPa pressure and correlates well with the TEP peak

Stability of the hcp phase and temperature variation of the axial ratio of iron near Earth-core conditions

We theoretically document the stability of hcp iron for pressure–temperature conditions of the Earth’s inner core by separately computing the electronic and phonon contributions to the free energy. These pseudopotential-based quasi-harmonic calculations reveal that the hcp phase remains stable compared to bcc and that the c/a ratio of lattice parameters exhibits only a modest temperature dependence at inner-core conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58123/2/cm7_1_016208.pd

On the nature of the dhcp to fcc transition under pressure in Pr and Pr-Th alloys

The results of electrical resistance (R), thermoelectric power (TEP) and X-ray diffraction measurements on praseodymium (Pr) and its alloys with thorium under pressure are reported. The maximum inR vsP curve exhibited by Pr persists only in the dhcp phase of PrTh alloy. X-ray measurements confirmed that in the alloys also the maximum inR vsP curve is due to the dhcp → fcc transition. Thus the behaviour of Pr and Pr-Th alloys is different from that of La and its alloys with Ce and Th where the maximum in theR vsP curve is electronic in origin and is exhibited by the dhcp, fcc and dist fcc phases

X-ray transport in a Ni plasma

The IEEOS form of Saha's equation has been solved for a Ni plasma with the resultant equation of state agreeing well with TFDEOS. Mean opacities are obtained from bound-bound, bound-free, free-free and scattering processes. The X-ray transport obtained in the optically thick limit is compared with the computed results of Mizui et al. and shows similar characteristics as seen experimentally by them for the transmittance

Computational condensed matter physics

In the high pressure laboratory at BARC, we are pursuing a program to study the behaviour of materials under static and dynamic pressures. Theoretical component has been an integral part for guiding and interpreting new experiments. The initial phase of such efforts was devoted to the development of equation of state models at arbitrary temperatures and matter densities. With the advent of diamond anvil cell device and the simultaneous provision for laser heating of the compressed samples for static high pressure studies, and with the improvements of the diagnostic techniques in dynamic shock methods, the focus of our studies switched over to the predictions and interpretations of phase transitions. Often these efforts have led to intense experimental studies and sometimes helped in resolving the controversies in data. We adopted the first principles electronic structure calculations for high pressure studies. Our work on the electronic topological transition in zinc led to many experimental and theoretical investigations. The results of electronic structure changes in similar metal cadmium shall be compared with existing understanding in Zn under pressure. Our studies on Nb and other compounds like intermetallics and borocarbides have revealed interesting electronic structure changes under pressure. However, the electronic structure based investigations of structural stabilities at high pressures involve tedious trial and error effort, which is avoided in the ab initio molecular dynamics simulations. The current status of our efforts in the use of this technique is illustrated with the example of quasicrystal based clusters