INSTTTUTE OF PHYSICS PUBLISHENG Elastic modulus J.Phys.:Condens.Matter 15 (2003)5307-5314 PLS953-898403162293-9 The elastic energy of a solid under strain is given by Ab initio elastic constants for the lonsdaleite phases of C,Si and Ge V 6 6 △E= SQ Wang and H Q Ye! Cijeiej GPa GPa Nb A-0.5 Fe A-2.4 150 V is the volume of the undistorted lattice cell,E is the energy 140 130 increment from the strain with vector e=(e,e2,e3,e,es,e6) 100 20 0 200 C is the matrix of the elastic constants. 100 100 100 0 100 100 160 For cubic phases--three independent elastic constants,Cu,C2 and C4; -100 0 0 100 -100 000 -100 100 140 For hexagonal phases--two more independent elastic constants,C13 and C33. The primitive vectors of a cubic diamond structure are defined as 一2 245 .(I+e) 0 22 学 22Elastic modulus The elastic energy of a solid under strain is given by V is the volume of the undistorted lattice cell, E is the energy increment from the strain with vector e = (e1 , e2 , e3 , e4 , e5 , e6 ). C is the matrix of the elastic constants. For cubic phases -- three independent elastic constants, C11, C12 and C44; For hexagonal phases -- two more independent elastic constants, C13 and C33. The primitive vectors of a cubic diamond structure are defined as