Stresses and elastic constants of crystalline sodium, from molecular dynamics
The stresses and the elastic constants of bcc sodium are calculated by molecular dynamics (MD) for temperatures to T = 340K. The total adiabatic potential of a system of sodium atoms is represented by pseudopotential model. The resulting expression has two terms: a large, strictly volume-dependent potential, plus a sum over ion pairs of a small, volume-dependent two-body potential. The stresses and the elastic constants are given as strain derivatives of the Helmholtz free energy. The resulting expressions involve canonical ensemble averages (and fluctuation averages) of the position and volume derivatives of the potential. An ensemble correction relates the results to MD equilibrium averages. Evaluation of the potential and its derivatives requires the calculation of integrals with infinite upper limits of integration, and integrand singularities. Methods for calculating these integrals and estimating the effects of integration errors are developed. A method is given for choosing initial conditions that relax quickly to a desired equilibrium state. Statistical methods developed earlier for MD data are extended to evaluate uncertainties in fluctuation averages, and to test for symmetry. 45 refs., 10 figs., 4 tabs.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5848410
- Report Number(s):
- LA-10342-T; ON: DE85011889
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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SODIUM
BCC LATTICES
THERMODYNAMIC MOLECULAR MODEL
CRYSTAL MODELS
ELASTICITY
ELECTRIC POTENTIAL
LATTICE PARAMETERS
NUMERICAL SOLUTION
STATISTICAL MODELS
THERMODYNAMICS
ALKALI METALS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
ELEMENTS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
METALS
MOLECULAR MODELS
TENSILE PROPERTIES
360602* - Other Materials- Structure & Phase Studies