Thermodynamics of the spin-1/2 antiferromagnetic uniform Heisenberg chain

We present a new application of the traditional thermodynamic Bethe ansatz to the spin-1/2 antiferromagnetic uniform Heisenberg chain and derive exact nonlinear integral equations for just two functions describing the element ary excitations. By using this approach, the magnetic susceptibility chi an d specific heat C versus temperature T are calculated to high accuracy for 5 x 10(-25), less than or equal to T/J less than or equal to 5. The chi(T) data agree very well at low T with the asymptotically exact theoretical low -T prediction of Lukyanov [Nucl. Phys. B522, 533 (1998)]. The unknown coeff icients of the second and third lowest-order logarithmic correction terms i n Lukyanov's theory for C(T) are estimated from the C(T) data.