Negative scattering length of ultracold ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ gas

We have improved the theoretical triplet ground-state potential of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}_2^{}{}_{}{}^{}$ by means of an inverse perturbation analysis, and find that the diatomic scattering length for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ atoms in the F=2, ${\mathit{m}}_{\mathit{F}}$=2 ground-state hyperfine level is negative. The consequences of this result for achieving Bose-Einstein condensation in a trapped ultracold ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ gas sample are addressed.