The first-order liquid-liquid phase transition in supercooled Si is revisited by long-time first-principle molecular dynamics simulations. As the focus of the present paper, its nature is revealed by analyzing the inherent structures of low-density liquid (LDL) and high-density liquid (HDL). Our results show that it is a transition between a sp(3)-hybridization LDL and a white-tin-like HDL. This uncovers the origin of the semimetal-metal transition accompanying it and also proves that HDL is the meta-stable extension of high temperature equilibrium liquid into the supercooled regime. The pressure-temperature diagram of supercooled Si thus can be regarded in some respects as shifted reflection of its crystalline phase diagram. (C) 2015 AIP Publishing LLC.
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