The charge distribution, Knight shift $K_s$, and total energy E of intermetallic LiTl and NaTl have been calculated by the relativistic augmented-plane-wave method. For the B32-phase NaTl it is found that the valence-electron bands are separated by a band gap. The lower valence bands are built up by the 6s electrons of Tl forming covalent s-like bands within the diamondlike Tl sublattice. These 6s bands give a negative contribution to $K_s$(Tl) of -0.52% due to the exchange polarization effect. The valence bands above the 6s bands are sp bands of predominantly metallic character. In the B2-phase LiTl all valence bands overlap and the covalent character of the lower valence bands is much less pronounced than in NaTl. Theoretically the following values for $K_s$ are found: $K_s$(LiTl) = 0.003%, $K_s$(LiTl)=1.0%, $K_s$(NaTl) = 0.002%, and $K_s$(NaTl)=-0.14%. The agreement with the experimental results is good besides $K_s$(NaTl) [$K_s$(expt., NaTl)=-0.96%]. From the shape of the electron bands near the Fermi surface one could conclude that the difference between $K_s$(theor., NaTl) and $K_s$(expt. NaTl) is caused by a diamagnetic contribution to $K_s$. To obtain some insight in the stability of Zintl phases (B32 structure), the energy difference ΔE=E(B2)-E(B32) is calculated. One obtains ΔE(LiTl) =-0.15 eV per atom and ΔE(NaTl)=+0.005 eV per atom. The physical mechanisms which lead to the different signs in ΔE are discussed.

• Received 17 September 1984

DOI:https://doi.org/10.1103/PhysRevB.31.5015