摘要:
本文使用第一性原理的GGA/RPBE方法研究了Cr_2MC（M=Al,Ga）的电子结构、弹性和热力学性质.研究发现两个化合物的体积压缩性几乎相同,并且证实了在0—50GPa范围内c轴始终较a轴更难以压缩并且结构始终是稳定的.通过对内坐标的研究发现了Cr_2AlC中Cr离子的内坐标始终大于Cr_2GaC中Cr离子的内坐标.使用准谐德拜模型得到的体弹模量在0GPa下随着温度的升高而减小,而在300GPa下则随着温度的升高而增大.对德拜温度的研究发现Cr_2GaC的值小于Cr_2AlC的值,而对热膨胀系数、Gr（u｜¨）neisen参数、熵和热容的计算发现Cr_2GaC的值大于Cr_2AlC的值.对电子结构的分析发现Cr_2GaC的s和p电子在费米能级处的值大于Cr_2AlC的s和p电子的值,而其他离子的电子分布几乎一致.
Abstract:
We investigate the electronic,elastic and thermodynamic properties of nanolaminate Cr_2MC（M=Al,Ga） by using the ab initio pseudopotential total energy method.Our results show that they have shown almost identical volume compressibilities.The axial compressibility investigations show that the c axis is always stiffer than a axis.The internal coordinate calculations revealed that the values of Cr atoms in Cr_2AlC are always larger than those in Cr_2GaC.The elastic constants calculations demonstrated the structural stability within 0—50 GPa.The obtained bulk moduli by quasi-harmonic Debye model observed that the bulk moduli of Cr2MC（M=Al, Ga）decrease with temperature at 0 GPa,but increase at 300 GPa.We also found that the Debye temperatures of Cr_2GaC are always smaller than those of Cr_2A1C at any conditions.However,the opposite cases can be found in thermal expansion coefficients,Griineisen parameter,entropy and heat capacity when comparing their respective counterparts between Cr_2GaC and Cr_2AlC.The electronic density of states and energy band distribution demonstrated that the Cr_2MC（M=Al,Ga） have shown similar profiles with the only exception of the more localized s and p electrons in Cr_2GaC than their respective counterparts in Cr_2AlC.
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