Convergence study of the partition function for methyl formate. Comparison of the partition function values computed in the present study (full red circles) and JPL database (full green squares). The linear interpolation of the partition function computed in the present study is given as red dashed lines while the nonlinear sixth-order polynomial fit is given as a blue line. From JPL, the linear interpolation and the nonlinear fit (green line) are apparently overlapped. The differences between the two partition functions are due to the fact that the JPL partition function does not include the vibrational contribution and does take into account the torsional contribution from Eq. (9) only up to v_t = 0 and 1, whereas we are including torsional levels up to v_t = 10 as well as the vibrational contribution.