**************** The 17th., Lab Seminar ****************************

Date: Mon, January 15, 2007  PM 4:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Yukinori Nakagawa 


Title: Structure and Dynamics of Hydrated NH4+: An ab initio QM/MM Molecular Dynamics Simulation
Intharathep, Tongraar, and Sagarik 
Journal of Computational Chemistry 26 (2005) 1329-1338

Abstract: 
 A combined ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulation has been performed 
to investigate solvation structure and dynamics of NH4+ in water.The most interesting region, the sphere includes an 
ammonium ion and its first hydration shell, was treated at the Hartree－Fock level using DZV basis set, while the rest 
of the system was described by classical pair potentials. On the basis of detailed QM/MM simulation results.The 
solvation structure of NH4+ is rather flexible, in which  many water molecules are cooperatively involved in the 
solvation shell of the ion. Of particular interest, the QM/MM results show fast translation and rotation of NH4+ in 
water. This phenomenon has resulted from multiple coordination, which drives the NH4+ to translate and rotate quite 
freely within its surrounding water molecules.In addition, a "structure-breaking" behavior of the NH4+  is well 
reflected by the detailed analysis on the water exchange process and the mean residence times of water molecules 
surrounding the ion.

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