The SOECs and TOECs. The strain-energies for Y[Ni.sub.2][B.sub.2]C, including the results of the first-principles calculations and the fitted polynomials, are shown in Figure 2.
It is found that our values of SOECs provide good agreement with the results obtained from the previous calculations and experiments, which provides guarantee for calculating the TOECs accurately.
It is helpful to describe the effective SOECs under different pressure using the SOECs and TOECs. The effective SOECs [C.sup.P.sub.ij] of a crystal can be obtained when subjected to pressure P.
The variation of the effective SOECs [C.sup.P.sub.ij] with pressure in the range of 0-5 GPa for Y[Ni.sub.2][B.sub.2]C on the basis of the calculated SOECs and TOECs is shown in Figure 4.