The expressions for second (SOE) and third order elastic (TOE) constants for rare gas solids are derived for comparative study of elastic behavior within the framework of many body potentials including the effect of pressure. The derived expressions are used to obtain the relations for pressure derivatives of bulk and shear moduli of RGS solids. The values of SOE, TOE constants and pressure derivative of bulk and shear modulus for Ne up to 100 GPa, Ar up to 75 GPa, for Kr up to 136 GPa and Xe up to 53.4 GPa pressure are computed. The results are in agreement with available experimental results. The computed results are then used to analyze the pressure up to high compression and the elastic and seismic wave velocities (P & S) in Earth's deep interior. elastic properties, seismic wave velocities, RGS

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A phenomenological lattice theory of elastic dielectric based on the Lundqvist potential of ionic cohesion is developed. In this theory the lattice is considered to be initially in the deformed and polarised state. The theory yields the expressions for the second order elastic constant, third order elastic constants, dielectric constants, and its strain derivatives. The many body lattice theory (MLT) of elastic dielectric so developed is applied to calculate the strain derivatives of the high and low frequency dielectric constants of the alkali halide solids. The calculated values of these constants are better than those obtained in all earlier models and are in excellent agreement with the experimental values.Es wird eine phanomenologische Gittertheorie elastischer Dielektrika entwickelt, die auf dem Lundqvistpotential fur die Ionenkohasion beruht. In dieser Theorie wird angenommen, daI3 das Gitter anfanglich im deformierten und polarisierten Zustand ist. Die Theorie liefert die Ausdrucke fur die elastischen Konstanten zweiter Ordnung, elastischen Konstanten dritter Ordnung, dielektrischen Konstanten und ihre Spannungsableitungen. Die so entwickelte Vielkorper-Gitter-Theorie (MCT) elastischer Dielektrika wird benutzt, um die Spannungsableitungen der Hoch-und Niederfrequenz-Dielektrizitatskonstanten der Alkalihalogenide zu berechnen. Die berechneten Werte dieser Konstanten sind besser als die, die mit allen fruherenModellen erhalten wurden, und stimmen ausgezeichnet mit den experimentellen Werten uberein.

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The elastic properties of alkaline earth oxides (AEOs) under high temperature are discussed within the framework of many body Lundqvist potential incorporating the contribution of thermal phonon pressure. The short-range repulsive interaction is taken up to the second nearest neighbors. The derived expressions are used to compute the values of second-order elastic constants (SOECs) and bulk modulus of alkaline earth oxides at different temperatures (300 • K-2000 • K). The results are found to be satisfactory and are in agreement with available experimental and the theoretical results.

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The quantum-dielectric-ion-dependent model for A "9' binary solids has been analyzed and used to predict the average energy gaps between the bonding and antibonding states. The results are in excellent agreement with the available experimental values.