Finite temperature simulations of the frustrated S=1/2 chains

Thermodynamical properties of the one-dimensional S = 1/2 Heisenberg model with dimerized nearest and uniform next-nearest neighbors interactions, app licable to CuGeO3 and Pb[CU(SO4)(OH)(2)] compounds, are studied by the nume rically exact quantum transfer-matrix method. Suzuki-Trotter formula is use d to obtain a classical system with spin sigma = 3/2 and effective interact ions between nearest neighbors only. Magnetic specific heat and magnetic su sceptibility curves are calculated and compared with experimental results i n a wide temperature range giving estimates of the coupling parameters in t he model proposed for CuGeO3 and Pb[CU(SO4)(OH)(2)].