• R V Gopala Rao

      Articles written in Pramana – Journal of Physics

    • Mean spherical model-structure of liquid argon

      R V Gopala Rao T Nammalvar

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      A new formulation forS(k), the structure factor, has been obtained, treating the square-well potential as a perturbation on the hard-core in the mean spherical model approximation. The potential parameters have been varied not only to get a satisfactory peak height at the fitted temperature but also over a wide range of temperatures and densities. The agreement between the computed and experimental structure factor values shows that the representation of the attractive tail by a square-well potential yields a satisfactory method in understanding the structure of liquid argon.

    • Self diffusion in liquid Na-K alloy

      R V Gopala Rao A K Murthy

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      Self diffusion coefficients,Di, in liquid Na-K alloy at 373 K have been computed in the linear trajectory approximation of Helfand, with square well as an attractive tail. From the computedDNa andDK, the mutual diffusion coefficient,DNaK has also been determined.DNa,DK andDNaK all increase with increase of concentration of potassium, while the ratio,DNa/DK remains constant (1.45 ± 0.01) over the entire concentration range.

    • Partial structures and compressibilities of ions in fused potassium bromide

      R V Gopala Rao Sobhen Kumar Pal

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      Treating the coulomb interaction between ion species as a perturbation on the Waisman-Lebowitz solution for direct correlation function within the hard core region, the total direct correlation function in K-space has been formulated, which gives a direct method of evaluating the partial structure factors between different ion species of the fused salts through the use of Pearson-Rushbrooke equations. The partial structure factors so obtained have been applied to evaluate the partial radial distribution functions of ion pairs. In addition, many other important associated functions such as the static correlations of total number, mass and charge densities have been computed by particular linear combination of partial structure factors. The charge neutrality relate the partial structure factors to the isothermal compressibility for the wavevectorK → 0 and hence the evaluation of the compressibilities of ions in fused KBr is possible, which agrees well with the observed value. As such the present method is very useful in investigating the structure of molten salts since only the parametersσij, the distances of closest approach between ions andɛ, the effective dielectric constant (which can be estimated from the literature) are enough for this work.

    • Computation of collective modes and acoustic investigations at different temperatures of vitrous silica

      R V Gopala Rao R Venkatesh

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      This paper is mainly concerned with elastic and acoustic properties of vitrous silica besides the computation of phonon frequencies. Thus the phonon frequencies of vitrous silica have been calculated assuming the electronic bulk modulus,Ke, as equal to zero. New equations have been derived to relate the pressure derivatives of second order elastic constants to the acoustic Gruneisen’s parameters using both Bhatia-Singh’s parameters and Schofield’s equations. The calculated longitudinal and transverse Gruneisen’s parameters and the predicted absorption band spectra from Nagendranath’s equation and Bhatia Singh’s parameters are in good agreement with experiment. The calculated mean acoustic mode Gruneisen’s parameter evaluated from the pressure derivative of Nagendranath’s equation is also in good agreement with experiment.

    • Computation of collective modes and acoustic investigations at different temperatures of vitrous silica

      R V Gopala Rao R Venkatesh

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    • Four constant potential function of amorphous selenium and evaluation of its thermodynamic and acoustic properties

      R Venkatesh R V Gopala Rao Sumita Bandyopadhyay

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      Litov and Anderson after various considerations suggested a four constant potential function for a-Se as well as a-As2S3. Hence we also used a four constant potential function with the sole purpose of applying this potential function to obtain several acoustic, thermodynamic and other properties. We calculated several acoustic properties of a-Se like second order elastic constants (SOECs), their pressure derivatives, the longitudinal and transverse Grüneisen constant by two different methods, phonon frequencies, absorption band position through the use of Nath-Smith-Delaunay’s equation, and the thermodynamic properties like heat capacity, bulk modulus, thermal Grüneisen constant, the pressure derivative of the bulk modulus (dKT/dP=C1), the pressure derivative ofC1 which is related to Anderson-Grüneisen parameter, pressure derivative of Grüneisen constant namelyγg which is related to second Grüneisen constant, characteristics of phonon frequencies, potential energy function through the use of fitted parameters and third order elastic constants. Finally we calculatedKT at the reduced density ofρ/ρ0=1.1.KT is obtained from the potential function with the fitted parameters. In all the above cases the calculated values are found to be in good agreement with experiment wherever available. In this connection it is important to point out that we eliminated ‘C’ a constant in the potential function using the equilibrium condition as was done by Litovet al in a-Se and Gerlichet al in the case of a-As2S3 as all amorphous substances are isotropic as mentioned by several authors. We contemplate to calculate several other properties for a-Se and a-As2S3 and present them at a later stage.

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