抄録
The interatomic potential derivatives related to higher-order force constants are formulated in the microscopic electronic theory.The convergence of the numerical integral in calculating the interatomic potential derivatives becomes worse as the degree of the differentiation increases.The difficulty of the convergence for the fourth derivative of the interatomic potential is overcome using the asymptotic form of the integral function.Numerical calculations are performed for practical material Al with low density and for alkali metal K with high density and with anharmonic characteristics.The accuracy of the interatomic potential derivatives obtained should be confirmed by considering non-integral term in addition to integral term.The interatomic potential derivatives as function of the atomic distance and under compression are calculated in connection with the convergence of the integral.The convergence of the numerical integral for the third and fourth derivatives of the interatomic potential related to the anharmonic property is established by increasing the upper limit, and the overall value Xm=10 as the upper limit of the non-dimensional wave number is proposed.
