中文摘要：

利用最新的粒子群优化算法,发现一种新型立方碳结构（命名为sc-C20,=4.886）,并对其性质及可能的合成方法进行了研究。在常压下sc-C20可以亚稳存在,当压力超过100GPa时,sc-C20比石墨稳定,表明其通过高压手段合成的可能性。通过对比晶格常数和晶面间距,发现sc-C20与实验合成的=4.86的i-碳结构相吻合,表明sc-C20有可能通过化学手段合成。电子能带结构计算表明sc-C20为宽带隙（4.20eV）半导体型碳,并且随着压力升高带隙呈现增大的趋势,sc-C20带隙的大小及变化规律与金刚石相似。sc-C20的体积模量和剪切模量很高,维氏硬度为94.4 GPa,与立方金刚石硬度相当。强度计算表明sc-C20抗拉强度的各向异性较弱,其中〈111〉方向的抗拉强度最高,为96.4 GPa。

英文摘要：

A novel cubic carbon（termed as sc-C20 with 4.886 ？ is proposed through employing the newly developed particle swarm optimization（PSO） algorithm.Furthermore,the properties and possible synthesis methods are investigated.The sc-C20 is metastable under ambient pressure,and is more stable than graphite at high-pressure（100 GPa）,indicating that it can be synthesized through high-pressure.The similarity of the lattice parameters and-spacing between sc-C20 i-carbon with 4.86 ？implies that the former can be achieved through chemical methods.Electronic band structure calculations show that sc-C20 is a semiconductor with wide band gap of 4.20 eV,and the gap increase with pressure,similar to that of diamond.The sc-C20 has high bulk and shear moduli,and the Vickers hardness is 94.4 GPa,comparable with that of diamond,indicative of superhard nature.The tensile strength of sc-C20 is low,and the highest strength is 96.4 GPa along 111 direction.