hcp-,fcc-和bcc-Sc晶格稳定性的第一原理研究

Study on lattice stability in first principles of hcp-,fcc- and bcc-Sc

分别采用第一原理总能赝势平面波的局域密度近似LDA(Localdensityapproximation)和广义梯度近似GGA(Generalizedgradientapproximation)两种近似方法计算hcp-,fcc-和bcc-Sc的晶格常数、总能和态密度,并将实验值与以上两种方法以及CALPHAD方法的计算结果进行对比研究,发现采用LDA和GGA的计算结果均为ΔGbcc-hcp>ΔGfcc-hcp>0,与CALPHAD方法外推的结果ΔGfcc-hcp>ΔGbcc-hcp>0不一致。用LDA方法计算的hcp-,fcc-和bcc-Sc的晶格常数和原子体积较GGA方法的计算结果小,但总能绝对值偏大。LDA方法与GGA方法的态密度曲线形状基本一致,但LDA得到的s和p态电子占据数比GGA方法的偏小。

The local density approximation（LDA） and general gradient approximation（GGA） of total energy plane wave pseudopotential method in first principles have been used to calculate the lattice constants, total energies and density of state of hcp-, fcc- and bcc-Sc. The results have been compared with both calculated results of CALPHAD method and experimental data. It is found that lattice stability parameters obtained by LDA and GGA in first principles are all ΔGbcc-hcp〉ΔGfcc-hcp〉0 but very different with the result of CALPHAD method as △G^fcc-hcp 〉 △G^bcc-hcp 〉 0. And the lattice constants and atomic volumes calculated in LDA are smaller than those in GGA. The absolute values of total energies in LDA are larger than those in GGA. The curve shape of state density in LDA is very similar with that in GGA. But, the electronic occupation number of hcp-, fcc- and bcc-Sc in s and p state calculated in LDA are less than that in GGA.