Roy Umesh C, Bongiorno Angelo
Department of Chemistry, College of Staten Island, Staten Island, New York 10314, United States.
The Graduate Center of the City University of New York, New York, New York 10016, United States.
J Phys Chem C Nanomater Interfaces. 2024 Dec 2;128(49):21220-21227. doi: 10.1021/acs.jpcc.4c06550. eCollection 2024 Dec 12.
Density functional theory calculations and a finite deformation method are used to calculate second- and, most notably, third-order elastic constants of amorphous silicon and amorphous silicon dioxide, as represented by model structures generated via melt-quench force-field molecular dynamics simulations. Linear and nonlinear elastic constants are used to deduce macroscopic elastic moduli, such as the bulk and shear moduli, their pressure derivatives, and the elastic Grüneisen parameter. Our calculations show that the elastic properties of amorphous silicon reach the isotropic elastic limit within the nanometer length scale, attaining characteristics, both linear and nonlinear, comparable to those of crystalline silicon. In contrast, the nonlinear elastic properties of silica retain an anisotropic character over the nanometer length scales, yielding nonetheless the expected pressure-induced softening of the elastic moduli. This atypical elastic behavior is correlated to the occurrence of long-wavelength acoustic modes with negative Grüneisen parameters.
采用密度泛函理论计算和有限变形方法，来计算非晶硅和非晶二氧化硅的二阶弹性常数，最值得注意的是三阶弹性常数，这些常数由通过熔体淬火力场分子动力学模拟生成的模型结构表示。线性和非线性弹性常数用于推导宏观弹性模量，如体积模量和剪切模量、它们的压力导数以及弹性格林爱森参数。我们的计算表明，非晶硅的弹性特性在纳米长度尺度内达到各向同性弹性极限，其线性和非线性特性与晶体硅相当。相比之下，二氧化硅的非线性弹性特性在纳米长度尺度上保持各向异性，不过仍会出现弹性模量预期的压力诱导软化。这种非典型的弹性行为与具有负格林爱森参数的长波长声学模式的出现有关。
