Both tetrahydrofuran （THF） and 2-methyltetrahydrofuran （MTHF） are studied systematically at desired temperatures using molecular dynamics simulations. The results show that the calculated densities are well consistent with experiment. Their glass transition temperatures are obtained： 115 K - 130 K for THF and 131 K - 142 K for MTHF. The calculated results from the dipolar orientational time correlation functions indicate that the ＂long time＂ behavior is often associated with a glass transition. From the radial and spatial distributions, we also find that the methyl has a direct impact on the structural symmetry of molecules, which leads to the differences of physical properties between THF and MTHF.
The adenine-thymine base pair was studied in the presence of hydroxyl radicals in order to probe the hydrogen bond effect. The results show that the hydrogen bonds have little effect on the hydroxylation and dehydrogenation happened at the sites, which are not involved in a hydrogen bond, while at the sites involved in hydrogen bond formation in the base pair, the reaction becomes more difficult, both in view of the free energy barrier and the exothermicity. With a 6-311 ＋＋G（d,p） level of description, both B3LYP and MP2 methods confirm that the C8 site of isolated adenine has the highest possibility to form covalent bond with the hydroxyl radicals, though with different energetics： B3LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the dehydrogenation reactions, B3LYP method predicts that the free energy barrier increases in the order of HN9 〈 HN61 〈 HN62 〈 H2 〈 H8.
Structural properties of the pure water and halogen solutions at high temperatures and pressures are studied by using the molecular dynamics simulations and quantum molecular simulations. The related characters are calculated as functions of temperature and pressure. The results show that the hydrogen bonded networks become looser as temperature increases,with the collapse of the traditional tetrahedral structure. It is similar to the concentration-dependent collapse in the Na Cl solutions. However, adding other halogen elements has no further effects on the already weakly bonded water molecules.At the phase changing points, the process of hydration is evident for the bigger ions, so that the bigger the ion is, the smaller a cluster is formed.
An improved isospin dependent Boltzmann Langevin model,in which the inelastic channels and momentum dependent interactions are incorporated,is used to investigate the high-density behavior of nuclear symmetry energy.By taking several forms of nuclear symmetry energy,we calculate the time evolutions of neutron over proton ratio,π multiplicity and π-/π+ ratio,and the kinetic energy and transverse momentum spectra of π-/π+ ratio in the heavy ion collisions at 400A MeV.It is found that the neutron over proton ratio and π-/π+ ratio are very sensitive to the nuclear symmetry energy,and the π-is more sensitive to the nuclear symmetry energy than the π+.A supersoft symmetry energy results in a larger π-/π+ ratio.
The temperature of fragmenting source in central heavy-ion collisions at Fermi energy is investigated by the isospin-dependent quantum molecular dynamics model in combination with the statistical decay model GEMINI.Five different nuclear thermometers are used to extract nuclear temperature.We find that the He and Li isotope temperature reaches a plateau at about 70-100 MeV/nucleon of beam energy.The slope temperature and the quadrupole fluctuation temperature give high values.The quantum slope temperature and the quantum quadrupole fluctuation temperature are more close to the He and Li isotope temperatures.
The work is devoted to the implementation of the hydrodynamic laws to the head-on heavy ion collisions within the energy range 50-100 MeV/A.The hydrodynamic mechanisms of the bubble and ring structures formation are investigated.It is shown that there is a possible hydrodynamic explanation of the different structures being formed in the case of soft(K=200 MeV) and stiff(K=400 MeV) equations of state.Within the suggested approach the final geometry of the system is defined in the initial stage of the collision and is very dependent on the sound velocity in the nuclear matter.The obtained results are in a good correspondence with the Boltzmann-like transport theory calculations and the experimental data for the selected energy range.
