Molecular Dynamics Simulation of High Temperature and Pressure Water

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1 Mar CHEMICAL INDUSTRY AND ENGINEERING 25 2 Vol. 25 No. 2 : (2008) ,, (, ) : (MD),,,,,, 5 % : ;;; ; :O :A Molecular Dynamics Simulation of High Temperature and Pressure Water DONG Yan2ping, DONG Xiu2qin, ZHANG Min2hua ( Key Laboratory for Green Chemical Technology, Ministry of Education, Tianjin University, Tianjin , China) Abstract :Microscopic structure, hydrogen2bond and self2diffusion properties of high temperature and pressure water were investigated by using molecular dynamics (MD) simulation. Moreover, the average geometrical configuration of water molecules at different state were analyzed. It was found that, with increasing temperature, the average number of hydrogen bond in water decreased, and the average geometrical configuration of water molecules changed regularly, bond length became shorter and H O H angle became larger. The changes were remarkable around the supercritical point. The microscopic structures of sub2critical and super2critical water were different from that of ambient water. The calculated self2diffusion coefficients of water agreed well with the experimental ones within less than 5 percent relative error. Key words :molecular dynamic (MD) simulation ; super2critical water ; microscopic structure ; hydrogen bond ; diffusion coefficient,(scw) [1 4],,, Kalinichev [5] BJ H SCW Nieto2Draghi [6] TIP4P SPCΠE TIP5P DEC4 COMPASS ( Condensed2phase Optimized Molecular Potentials for Atomistic Simulation Studies) [7], : : ( ),,, :, : (022) ,E2mail edu. cn

2 25 2 : fs (1 fs = s), MD,, COMPASS [8,9] 300 ps, 100 ps 1 MD MD [10 ],,,,, 2 MD 256,, (ab initio) COMPASS,, Maxwell2Boltzmann Group based, Velocity2Verlet [11 ] NVT, [12 ],, 200 ps NVE, 200, 3,, Group based [9 ] Ewald [13 ], 1 2 Πnm 1 Π( ) Πcm - 1 Πcm - 1 Πcm - 1 MD [14 ] [14 ] [15 ] [15 ] [15 ] Π D MD D Exp. TΠK Π(g cm - 3 ) h 10 9 Π(m 2 s - 1 ) 10 9 Π(m 2 s - 1 ) % Group based Ewald [16 ] Group based Ewald [17 ] Group based Ewald [17 ] Group based Ewald [18 ] , 2, Group based, 5 %,, Group based Ewald, Ewald Group based, (vdw) (Coulomb)

3 Group based 311, (Ridial distribution function, RDF) r : g ( r) = ( r) : ( r) r ; (4) 1 4 O O H, 25 MPa ; TΠK: ; ; K O H 25 MPa, TΠK: ; ; K O H 25 MPa, TΠK: ; ; K O O 25 MPa K g OH ( r) nm nm ( 1) ; 25 MPa K g OH ( r) nm,01205 nm,01215 nm, 25 MPa, TΠK: ; ; K O O nm ( 2),,,O H,, 1 2, 2 g OH ( r)

4 25 2 : 163 1,, ( T c = K) ( P c = 2118 MPa), K K, g OH ( r), K,,, ;, 3 4,,, g oo ( r),,,, 312, [19 ], O H r OH 0124 nm, O O H < 30 ( 5 ) n HB , Gu rdia [20 ] 3,,,,,,,,,,,,,,, 3 Π nm Π ( ) K,011 MPa K,25 MPa K,25 MPa K,25 MPa K,25 MPa K,25 MPa K,25 MPa K,300 kgπm K,300 kgπm K,300 kgπm K,300 kgπm : Green2 Kubo Einstein Einstein [21 ], D self D self N 1 = lim t 6 Nt r i ( t) - r i (0) 2 (5) i = 1,r i ( t),, 1Π6, 6 7 pπmpa : 23 ; 25 ; 27 ; 29 6

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