We report a theoretical study of Feshbach resonances in 6Li + 23Na
and 7Li + 23Na mixtures at ultracold temperatures using new accurate
interaction potentials in a full quantum coupled-channel calculation. Feshbach
resonances for l=0 in the initial collisional open channel 6Li(f=1/2,mf=1/2)+23Na(f=1,mf=1) are found to agree with previous
measurements, leading to precise values of the singlet and triplet scattering
lengths for the 6,7Li+23Na pairs. We also predict additional Feshbach
resonances within experimentally attainable magnetic fields for other collision
channels.Comment: 4 pages, 3 figure