An empirical potential of binary molecular clusters of (NH₃)_m(H₂O)₄ is proposed.Stable model structures of NH₃(H₂O)₄ are optimized by using a fast molecular dynamics algorithm.The optimal structures are refined by using conventional ab initio optimization method.Optimization and frequency calculations are carried out at different levels of density functional theory (DFT/B3LYP) and Mller-Plesset second-order perturbation method(MP2) with 6-311++G** basis set.It is found that stable model structures remain the minima at B3LYP and MP2 levels.12 new ab initio stable isomers of NH₃(H₂O)₄,including the second and third ones are obtained.The results show that there is no inevitable relevancy between stability and dipole moment,and the number of hydrogen bonds of isomers.

A simulated annealing method is used to study the microphase separation and crystallization in cylinder-forming semicrystalline diblock copolymers.The final structure depends on the relative strength of the microphase separation and the crystallization of one block copolymers.As the interblock segregation strength is relatively weak,crystallization disrupts cylindrical microphase.As the interblock segregation strength is sufficiently strong,crystallization is effectively confined within cylindrical domains formed by microphase separation in the melt.A range of intermediate segregation strength exists between the two cases,in which the crystallization is templated but not wholly confined within the nanoscale domains prescribed by microphase separation.The melt morphology is mostly retained in cooling,and the local distortions and connections between cylinders occur due to crystallization.The simulation is consistent with recently reported experimental results.In addition,as the interblock segregation strength is very strong,the crystallization is restrained which results in amorphous structures.