  Abstract Our ab initio all-electron relativistic Dirac-Fock (DF) calculations
for seaborgium hexacarbonyl Sg(CO)6 and seaborgium hexaisocarbonyl Sg(OC)6
predict atomization energies of 68.80 and 64.30 eV. Our Dirac-Fock-Breit-Gaunt
(DFBG) calculations for Sg(CO)6 and Sg(OC)6 yield atomization energies of 69.18
and 64.77 eV. However, our calculated non-relativistic (NR) Ae for Sg (CO)6 and
Sg(OC)6 are 68.46 and 62.62 eV. The calculated isomerization energies at the
DFBG, DF, and NR levels are 4.41,4.50 and 5.83 eV. The contribution of
relativity to the Eiso is - ~1.33 eV. The optimized bond distances Sg-C and C-O
for octahedral Sg(CO)6 using our DF (NR) calculations are 2.151 ( 2.318 and
1.119 ( 1.114 (ang}). The optimized six Sg-O and C-O bond distances for
octahedral Sg(OC)6 at the DF level are equal to 4.897 and 1.108 {ang}. However,
the optimized four Sg-O bond distances for the octahedral Sg(OC)6 at the NR
level are 5.160 {ang} each, and two Sg-O bonds of 2.721 {ang} each, but all six
C-O bonds are 1.108{ang} each. The energies at the DF level of theory for the
reaction Sg+6CO to yield Sg (CO)6 and Sg(OC)6 are calculated as -7.30 and -2.80
eV. Moreover, the energies of the reaction at the DFBG level to yield Sg(CO)6
and Sg(OC)6 are very close to those predicted at the DF level of theory of
-7.17 and -2.76 eV. However, the NR energies of the above-mentioned reaction
are -6.99 and -1.15 eV. The mean bond energies predicted for Sg(CO)6 with our
DF, DFBG, and NR calculations are 117.40 , 115.31, and 112.41 kJ/mol, whereas
the mean bond energies calculated for the isomer Sg(OC)6 at DF, DFBG and NR
levels are 45.03 ,44.39 and 18.49 kJ/mole. The predicted existence of both the
isomers with Eiso of ~ 4.50 and ~ 5.80 eV, may cause problems for experimental
identification of seaborgium hexacarbonyl.
