单质Si晶格稳定性的第一原理研究

采用SGTE纯单质数据库中Gibbs能的表达式, 结合JANAF热力学数据, 采用最小二乘法对SGTE纯单质数据库中元素Si的Gibbs能表达式进行了重新评估, 得到了比SGTE数据库更精确的结果; 同时, 将SGTE数据库中CALPHAD方法得到的晶格稳定参数外推至0 K, 与第一原理总能赝势平面波和投影缀加波方法的结果进行了对比, 发现第一原理总能赝势平面波方法得到的晶格稳定参数结果为 ＞ ＞ ＞0, 与CALPHAD方法外推结果一致. 同时, 研究发现: 第一原理总能平面波赝势方法计算的diamond-Si的晶格常数和原子体积比实验值大, fcc-, hcp-和bcc-Si的结果比第一原理投影缀加波方法的小, 总能绝对值出现了类似的结果; 四种结构中所有的价态电子密度分布到0至－15 eV区间, 部分s态电子转化为p态电子, 其中diamond-Si的转化数目最多, 结构最稳定, 这与电子态密度的计算结果一致.

First Principles Study of the Lattice Stabilities of Elemental Si

Taking the form of Gibbs energy functions in the SGTE (Scientific Group Thermodata Europe) database of pure elements, adopting the newly available thermochemical reference data of JANAF (Joint Army-Navy-Air Force) database, the correction of transition data and reassessment of the parameters of Gibbs energy of elemental Si have been performed with the least-square method. The results agree more accurately with JANAF data than with the SGTE data. At the same time, the lattice stability parameters obtained by the CALPHAD method in the SGTE database have been extrapolated to 0 K, and these results have been compared with those of the total energy plane wave pseudopotential method and projector augmented wave method in first principles．It was found that the result of the total energy plane wave pseudopotential method agrees with that of CALPHAD, ＞ ＞ ＞0. Besides, it was found that the results of lattice constants and atomic volumes of diamond-Si calculated by the total energy plane wave pseudopotential method were much larger than experimental data and those of fcc-, hcp- and bcc-Si were smaller than those by the projector augmented wave method in first principles. The same case occurred in total energy calculations. All the electrons in valence distribute in the energy zone from －15 to 0 eV, part of s state electrons per atom in diamond-, fcc-, hcp-, and bcc-Si are changed into p state electrons, and diamond-Si has the largest number of transition and is the most stable phase, which were further proved by the results of density of state calculations.