| Research Abstract |
The purpose of this study is to establish first-principles calculation of phonon-phonon interactions and the related macroscopic quantities such as thermal conductivities, aimed at surveying materials possessing high thermal conductivity.
During the period of study (2000-2003), I have made several pieces of progress in this field. First, a code of first-principles phonon calculation has been written. This code is written so as to match calculation of any crystals, and hence it was released to public as the name "Osaka2000".
In order to see the effects of phonon-phonon interactions, the program code is developed to treat pressure dependence of phonons, thermal expansion, etc. The basic procedure to obtain phonon life-time from these data of phonon-phonon interactions had been established. But, the feasibility of calculation by first-principles code was not certain. In this study, we showed that this is indeed possible at a level of some modifications to our program code. However, judicious use of linear response theory in this subject is yet fully exploited. This issue is a remaining problem.
Meanwhile, another approach of calculation of transport coefficients, though time-dependent correlation functions obtained by molecular dynamic simulations, has been examined. The basic strategy has been established in our code. However, the ability of our calculation is still not enough to resolve details of transport coefficients in terms of both the time scale and the space scale.
In real materials, I have examined the above basic procedures, and estimated phonon life-times. By estimation in this way, I have shown physical mechanism of individual materials, which were otherwise not clarified.
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