  The isoscalar giant monopole resonance (ISGMR) in Sn isotopes and other
nuclei is investigated in the framework of the isospin-dependent quantum
molecular dynamics (IQMD) model. The spectrum of GMR is calculated by taking
the root-mean-square (RMS) radius of a nucleus as its monopole moment. The peak
energy, the full width at half maximum (FWHM), and the strength of GMR
extracted by a Gaussian fit to the spectrum have been studied. The GMR peak
energies for Sn isotopes from the calculations using a mass-number dependent
Gaussian wave-packet width $\sigma_r$ for nucleons are found to be
overestimated and show a weak dependence on the mass number compared with the
experimental data. However, it is found that experimental data of the GMR peak
energies for $^{56}$Ni, $^{90}$Zr, and $^{208}$Pb as well as Sn isotopes can be
nicely reproduced after taking into account the isospin dependence in isotope
chains in addition to the mass number dependence of $\sigma_r$ for nucleons in
the IQMD model calculation.
