| In this thesis we further develop and improve the improved quantum molecular dynamics (ImQMD) model, and study the dynamical nucleus-nucleus potential at short distances and the dynamical potential energy surface of heavy fusion system.The main considerations include:(1) The energy constraint in the phase space occupation constraint method. In this thesis we introduce an energy constraint in the phase space occupation constraint. This additional constraint can further improve the stability of an individual nucleus(reducing the spurious emission of nucleons), and is helpful for the study of the formation process of the compound nuclei which lasts several thousand fm/c or longer. We have checked that the total energy of system is well conserved for thousands of fm/c with this new procedure. (2) The kinetic energy of nuclear system is reasonably well described by the extended Thomas-Fermi approxi-mation in the calculation of nucleus-nucleus potential. Based on the the kinetic energy expression T=(?)(p_i~2)/(2m) of a series of nuclei in the ground state and the kinetic energy expression of a tree Fermi gas, we describe the kinetic energy of an individual nucleus in the ImQMD model with the extended Thomas-Fermi approximation(EkETF), we find that the extended Thomas-Fermi approximation can reasonably well describe the ki-netic energy for finite nuclei from light to heavy nuclei around theβ-stability line. we give the expression of the extended Thomas-Fermi approximation(EkETF) for the potential energy parameters set IQ2 and IQ1, respectively. Furthermore, we calculate the kinetic energy factorξwhich locates in a reasonable range 0.4～0.6.Based on the ImQMD model and the extended Thomas-Fermi approximation of the kinetic energy, we study the dynamical nucleus-nucleus potentials for fusion re- actions 40Ca+40Ca,48Ca+208Pb and 126Sn+130Te. The results show that:(a) The dynamical Coulomb barrier strongly depends on the incident energy. (b) The depth of fusion pocket changes with the system of light or heavy. In addition, it is encouraging that the obtained barrier height and the depth of the fusion pocket are compara-ble with the results of the TDHF calculations, and the depth of the fusion pocket is about 25 MeV for this reaction system 40Ca+40Ca; The depth of the fusion pocket for 48Ca+208Pb is about 7 MeV which becomes much shallower than that of 40Ca+40Ca and the fusion pocket for 126Sn+130Te almost disappears, which indicates that quasi-fission could easily occur in heavy fusion process especially for the more symmetric systems. (c) The dynamical nucleus-nucleus potential at short distances are higher than the value of - Qgg since the composite system formed during the collision is ex-cited state not a real ground state. (d) The dynamical nucleus-nucleus potential for the fusion reaction 40Ca+40Ca at short distances are lower than the Coulomb barrier based on the frozen density; but the dynamical nucleus-nucleus potentials for the re-actions 48Ca+208Pb and 126Sn+130Te at short distances are higher than the Coulomb barrier based on the frozen density, which is quite different from the case of 40Ca+40Ca. These calculations indicate:additional incident energy which is so-called extra-push energy beyond the energy to overcome the Coulomb barrier may be required to form the compound nucleus for heavy fusion system. (e) The time to form composite system is different for different systems. For the fusion reaction 40Ca+40Ca with the incident energies above the Coulomb barrier, the spherical composite system is rapidly formed after the two nuclei touching. But for the two heavy fusion systems 48Ca+208Pb and 126Sn+130Te, the strongly deformed composite systems or called di-nuclear systems are formed at about t= 350 fm/c and can last hundreds even thousands fm/c, during these process the composite system tends to undergo quasi-fission or fission and the nuclear exchange are slower. Furthermore, based on the shell correction energy calculations with the Strutinsky shell correct method and deformed Woods-Saxon potential, we study the dynamical potential energy surface considering the shell correction energy. We study the dynamical potential energy surface of two heavy systems:we adopt twenty-three central collision reaction systems which lead to the same compound nu-cleus 256No, and twenty-four central collision reaction systems which lead to the same compound nucleus A=292, Z=114. We find that the shell effects and the dynamic effects strongly influence the dynamical potential energy surface especially at short distance.
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