報告書番号

Q10010

タイトル（和文）

内包原子種がシリコンクラスレート格子熱伝導率に及ぼす影響 -古典分子動力学法による検討-

タイトル（英文）

The Effects of Guest Atomic Species in Silicon Clathrates on the Thermal Conductivity Studied by using Classical Molecular Dynamics Simulations

概要 （図表や脚注は「報告書全文」に掲載しております）

本報告では, 古典分子動力学法を用いたシリコンクラスレートの格子熱伝導率の算出手法を開発し, シリコンクラスレートの格子熱伝導率と内包原子種との関係を調べた. 第一原理計算によって, 内包原子(Li, Na, K, Rb, Cs, Be, Mg, Sr, Ba) をクラスレート中のシリコン篭構造内で移動させたときのポテンシャル曲線を得て, これを再現するようにMorse ポテンシャルを作製した. Li 原子を篭内で移動させた場合, ポテンシャル曲線は2つの谷を示したのに対し, その他の原子の場合は1 つの谷しか示さなかった. 計算から得られたheat current ベクトルの自己相関関数にGreen-Kubo の方法を適用することによって, これらの原子を内包するシリコンクラスレートの格子熱伝導率を得た. ポテンシャル曲線が1つの谷を示す原子を内包するシリコンクラスレートの格
子熱伝導率は, 内包原子の単振動の周波数相当の値と正の相関を示した. ポテンシャル曲線が2つの谷を示す原子を内包するシリコンクラスレートの格子熱伝導率は総じて低くなった.

概要 （英文）

In this study, a numerical method to obtain thermal conductivity of a silicon clathrate was developed, and the effects of contained guest atomic-species in silicon clathrates on the thermal conductivity were studied. Classical molecular dynamics (CMD) calculation was selected as a numerical method. The interaction between a host silicon atom and a guest atom (Li, Na, K, Rb, Cs, Be, Mg, Sr, and Ba) was described by a Morse-type potential. The parameters of the potentials were newly developed in this study so that potential-curves were reproduced. The potential-curves were obtained from first-principles calculations when a guest atom was moved in a silicon cage. Their thermal conductivity could be obtained by using the Green-Kubo method. As a result, it is found that the thermal conductivity of the silicon clathrate involving Li atoms was low as a whole. The reason may be because, among the guest atoms, only Li atom had two minimum points in the potential-curve due to its relatively small atomic radius to a silicon cage. It is also found that the obtained thermal conductivity increases as 1/(2pi)(k/m)^0.5 increases when the guest atom is one minimum point in its potential curve . It is noted that m and k indicate atomic weight of a guest atom and a force constant of that in silicon cages, respectively. This relation is also found at the range over 3THz even ifmwas artificially changed. However, at the range under 3THz, the obtained thermal conductivity decreases as 1/(2pi)(k/m)^0.5 increases.

報告者

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