Formation Energies of the Intermetallic Compounds at the Ground and Thermally Excited States Determined by the ab initio Energetic Calculation and Calorimetric Measurement

摘要

To provide for the future progression of the theoretical calculations beyond the adiabatic approximation by taking account of not only the electronic wave functions but also the nuclear wave functions, the formation energy Delta E-f(total) determined experimentally from the ground state to the thermally excited state is inevitably necessary. In the present study, for each intermetallic compounds of the Mg-Zn and Mg-La binary systems, the standard enthalpy of formation, Delta H-f(T)o, which is defined as the sum of Delta E-f(total) and the volume work, p Delta V-f, was determined from 2 K to high temperature by combining solution calorimetry with heat capacity measurement. Because the p Delta V-f term for solids is negligibly small, the Delta E-f(total) values at T are approximately equal to the measured Delta H-f(T)o values. Thus the Delta E-f(total) values obtained extrapolated to 0 K from the data measured near 2 K were consistent with ones obtained by the ab initio FLAPW energetic calculation. Temperature dependences of the Delta E-f(total) values were small below 20 K. However, the Delta E-f(total) values over 20 K decreased linearly as a function of temperature due to the enhanced lattice vibration. In the near future, the Delta E-f(total) values obtained in the present study will be used for constructing the nuclear wave functions in solids.