  Configuration Interaction (CI) calculations on the ground state of the C atom
are carried out using a small basis set of Slater orbitals [7s6p5d4f3g]. The
configurations are selected according to their contribution to the total
energy. One set of exponents is optimized for the whole expansion. Using some
computational techniques to increase efficiency, our computer program is able
to perform partially-parallelized runs of 1000 configuration term functions
within a few minutes. With the optimized computer programme we were able to
test a large number of configuration types and chose the most important ones.
The energy of the $^3{\rm P}$ ground state of carbon atom with a wave function
of angular momentum L=1 and M$_{\rm L}$=0 and spin eigenfunction with S=1 and
M$_{\rm S}$=0 leads to -37.83526523 h, which is millihartree accurate. We
discuss the state of the art in the determination of the ground state of the
carbon atom and give an outlook about the complex spectra of this atom and its
low-lying states.
