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轉(zhuǎn)帖:Cubic以及Trigonal cell彈性常數(shù)的計算 已有11人參與
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原文地址:http://cyh.xjtu.edu.cn/bbs/viewt ... p;extra=&page=1 Cubic和Trigonal晶體的彈性常數(shù)個數(shù)比較少,計算擬核也比較方便,目前計算彈性常數(shù)主要有兩個思路,一個是應(yīng)力-應(yīng)變曲線關(guān)系,此外就是應(yīng)變能-應(yīng)變關(guān)系,在兩種情況下彈性常數(shù)都是曲線的一階導(dǎo)數(shù)。在計算過程采用那種關(guān)系來擬核彈性常數(shù)沒有什么確定標準,目前實際上最大的限制是很多DFT計算軟件實際上不能把應(yīng)變結(jié)構(gòu)應(yīng)變能轉(zhuǎn)換成應(yīng)力張量形式,如DMOL,Crystal,Wine2K等都不具備這個計算功能,CASTEP是少數(shù)直接可以輸出應(yīng)力的軟件,因此在CASTEP中采用了Stress-Strain關(guān)系來擬和彈性常數(shù): 首先給出MS擬核彈性常數(shù)文件的格式: Elastic constants from Materials Studio: CASTEP =============================================== Summary of the calculated stresses ********************************** Strain pattern: 1 (應(yīng)變方式) ====================== Current amplitude: 1 (第一種應(yīng)變模式,三軸主應(yīng)變,x-y方向壓縮,z方向拉伸,為一個Volume conserving mode) Transformed stress tensor (GPa) : 0.523249 0.000000 0.000000 0.000000 0.523249 0.000000 0.000000 0.000000 1.574015 Current amplitude: 2 (第二種應(yīng)變強度,三軸主應(yīng)力模式,Volume Conserving Mode) Transformed stress tensor (GPa) : -0.468860 0.000000 0.000000 0.000000 -0.468860 0.000000 0.000000 0.000000 -1.384910 Stress corresponds to elastic coefficients (compact notation): 8 8 3 0 0 0 as induced by the strain components: 3 3 3 0 0 0 Stress Cij value of value of index index stress strain 1 8 0.523249 -0.003000 1 8 -0.468860 0.003000(Hooke 定理擬核,應(yīng)力-應(yīng)變關(guān)系) C (gradient) : 165.351500 (彈性常數(shù)是Stress-strain曲線的一階倒數(shù),即Gradient) Stress intercept : 0.027194 2 8 0.523249 -0.003000 2 8 -0.468860 0.003000 C (gradient) : 165.351500 Stress intercept : 0.027194 3 3 1.574015 -0.003000 3 3 -1.384910 0.003000 C (gradient) : 493.154167 Stress intercept : 0.094552 Strain pattern: 2 (第二種應(yīng)變模式,三軸主應(yīng)力+剪切應(yīng)力) ====================== Current amplitude: 1 Transformed stress tensor (GPa) : 1.367027 0.000000 0.000000 0.000000 0.352390 0.264719 0.000000 0.264719 0.469198 Current amplitude: 2 Transformed stress tensor (GPa) : -1.382814 0.000000 0.000000 0.000000 -0.399398 -0.258369 0.000000 -0.258369 -0.455322 Stress corresponds to elastic coefficients (compact notation): 1 7 8 4 0 0 as induced by the strain components: 1 1 1 4 0 0 Stress Cij value of value of index index stress strain 1 1 1.367027 -0.003000 1 1 -1.382814 0.003000 C (gradient) : 458.306833 Stress intercept : -0.007893 2 7 0.352390 -0.003000 2 7 -0.399398 0.003000 C (gradient) : 125.298000 Stress intercept : -0.023504 3 8 0.469198 -0.003000 3 8 -0.455322 0.003000 C (gradient) : 154.086667 Stress intercept : 0.006938 4 4 0.264719 -0.002121 4 4 -0.258369 0.002121 C (gradient) : 123.293024 Stress intercept : 0.003175 ============================ Summary of elastic constants ============================ id i j Cij (GPa) 1 1 1 458.30683 +/- 0.000 3 3 3 493.15417 +/- 0.000 4 4 4 123.29302 +/- 0.000 7 1 2 125.29800 +/- 0.000 8 1 3 161.59656 +/- 0.000 ===================================== Elastic Stiffness Constants Cij (GPa) (勁度張量) ===================================== 458.30683 125.29800 161.59656 0.00000 0.00000 0.00000 125.29800 458.30683 161.59656 0.00000 0.00000 0.00000 161.59656 161.59656 493.15417 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 123.29302 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 123.29302 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 166.50442 ======================================== Elastic Compliance Constants Sij (1/GPa) (順度張量) SijCij=I (Uinty) ======================================== 0.0025481 -0.0004548 -0.0006860 0.0000000 0.0000000 0.0000000 -0.0004548 0.0025481 -0.0006860 0.0000000 0.0000000 0.0000000 -0.0006860 -0.0006860 0.0024773 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0081108 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0081108 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0060058 Bulk modulus = 255.08759 (GPa) (體彈性模量) Compressibility = 0.00392 (1/GPa) (壓縮系數(shù)) Axis Young Modulus Poisson Ratios (Young模量和Poisison比) E平均值=1/3(Ex+Ey+Ez),同理v=1/3(vxy+vxz+vyz) (GPa) X 392.44290 Exy= 0.1785 Exz= 0.2692 Y 392.44290 Eyx= 0.1785 Eyz= 0.2692 Z 403.66400 Ezx= 0.2769 Ezy= 0.2769 Lame constants for isotropic material (GPa) (Lambe各向異性常數(shù)和剪切模量Mu) Lambda = 194.5290, Mu = 137.6968 因此可以看到在擬核這個晶體的彈性常數(shù)的時候采用了兩種應(yīng)變模式,每種應(yīng)變模式計算了兩個應(yīng)變強度下的應(yīng)力,從而采用線彈性理論計算了與特定應(yīng)變模式有關(guān)的彈性常數(shù)。下面來說明應(yīng)變模式和彈性常數(shù)之間的關(guān)系: |
第一原理資料匯編 | 科研相關(guān)資料 | 第一原理 | 我的分享 |

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