Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Atom transfer radical polymerization.

New polymer synthesis by nitroxide mediated living radical polymerizations.

Metal-catalyzed living radical polymerization.

Controlled/living radical polymerization: Features, developments, and perspectives

Polymerization of Methyl Methacrylate with the Carbon Tetrachloride/Dichlorotris- (triphenylphosphine)ruthenium(II)/Methylaluminum Bis(2,6-di-tert-butylphenoxide) Initiating System: Possibility of Living Radical Polymerization

Iron(II) bis(triphenylphosphine)dichloride [FeCl2(PPh3)2] induced living radical polymerization of methyl methacrylate (MMA) in conjunction with organic halides as initiators [R−X:  CCl4, CHCl2COPh, (CH3)2CBrCO2C2H5, and CH3CBr(CO2C2H5)2] in the absence or presence of Al(OiPr)3 in toluene at 80 °C. The added aluminum compounds were not needed for the Fe(II)-mediated living polymerization unlike the RuCl2(PPh3)3-based counterpart. With CH3CBr(CO2C2H5)2 as initiator, the number-average molecular weights of polymers increased in direct proportion to monomer conversion, and the MWDs were narrow throughout the reactions (Mw/Mn = 1.1−1.3). The polymers possessed one initiator moiety at the α-end per one polymer chain. The tacticity was similar to that prepared by AIBN. These results indicate that the Fe(II) complex is effective in the homolytic and reversible cleavage of the carbon−halogen terminal originating from the halide initiators into a transient radical growing species to induce living MMA polymerization.

Iron(II) Chloride Complex for Living Radical Polymerization of Methyl Methacrylate1

Nickel(II) bis(triphenylphosphine)halides [NiX2(PPh3)2; X = Cl, Br] were employed for possible living radical polymerization of methyl methacrylate (MMA) in conjunction with an organic halide as an initiator [R−X:  CCl4, CCl3Br, and (CH3)2CBrCO2C2H5] in the presence of Al(OiPr)3 in benzene at 80 °C. The bromide-based initiating system [CCl3Br/NiBr2(PPh3)2] gave living polymers with narrow molecular weight distributions, whereas the chloride-based system [CCl4/NiCl2(PPh3)2] led to bimodal molecular weight distributions. The systems involving chloride and bromide [CCl4/NiBr2(PPh3)2 and CCl3Br/NiCl2(PPh3)2] failed to induce living polymerizations. The polymers obtained with (CH3)2CBrCO2C2H5/NiBr2(PPh3)2 were also living and possessed one initiator moiety at the α-end per polymer chain, which indicates the polymerization proceeds via the activation of the C−Br terminal by the nickel(II) bromide complex.

Nickel-Mediated Living Radical Polymerization of Methyl Methacrylate1

Living Radical Polymerization of Methyl Methacrylate with Ruthenium Complex: Formation of Polymers with Controlled Molecular Weights and Very Narrow Distributions1

Masami Kamigaito

Papers

Metal-catalyzed living radical polymerization.

Polymerization of Methyl Methacrylate with the Carbon Tetrachloride/Dichlorotris- (triphenylphosphine)ruthenium(II)/Methylaluminum Bis(2,6-di-tert-butylphenoxide) Initiating System: Possibility of Living Radical Polymerization

Iron(II) Chloride Complex for Living Radical Polymerization of Methyl Methacrylate1

Nickel-Mediated Living Radical Polymerization of Methyl Methacrylate1

Living Radical Polymerization of Methyl Methacrylate with Ruthenium Complex: Formation of Polymers with Controlled Molecular Weights and Very Narrow Distributions1