Calculated  Other theory  Expt.  
Ba2  4.712  4.72   
BaO  2.066  2.09  1.940 
Ba2 (Expt.)  It seems that the experimental value is unknown. 
Ba2 (Theory)  Q. Wang, Q. Sun, JZ. Yu, BL. Gu, Y. Kawazoe, and Y. Hashi, Phys. Rev. A 62, 63203 (2000) 
BaO (Expt.)  E. Tiemann, M. Bojaschewsky, C. SauterServaes, and T. Torring, Z. Naturforsch. A, 29, 1692 (1974) 
BaO (Theory)  Q. Wang, Q. Sun, JZ. Yu, BL. Gu, Y. Kawazoe, and Y. Hashi, Phys. Rev. A 62, 63203 (2000) 
Calculation conditions 

Version  OpenMX1.6 
Basis set  Ba9.0s2p2d1, O5.0s2p2d1 
Pseudo potential  Ba_GGA.vps, O_GGA.vps as scalar relativistic VPS 
Functional  GGAPBE 
spinorbit coupling  None 
Spin noncollinearity  None 
Ecut  200 Ryd 