Table 1 Elastic constants and bulk modulus in the Voigt-Reuss-Hill (VRH) approximation [as this is appropriate for polycrystalline samples (36)] of the most stable polymorphs calculated with the LDA (9) and RPA (22–26) methods.

LDA results are very close to those from RPA, showing the suitability of LDA for estimating second energy derivatives. Results are in units of gigapascal.

		C₁₁	C₂₂	C₃₃	C₁₂	C₂₃	C₁₃	B_VRH
c-BN	LDA	997	997	997	101	101	101	402
c-BN	RPA	968	968	968	81	81	81	378
h-BN(AA′)	LDA	923	926	28	174	3	3	138
h-BN(AA′)	RPA	910	915	29	153	−4	−5	131
m-BN	LDA	751	839	45	156	100	68	160
m-BN	RPA	745	830	43	137	90	58	151