The calculation of the viscosity from the autocorrelation function using molecular and atomic stress tensors
نویسندگان
چکیده
The stress± stress correlation function and the viscosity of a united-atom model of liquid decane are studied by equilibrium molecular dynamics simulation using two diŒerent formalisms for the stress tensor : the atomic and the molecular formalisms. The atomic and molecular correlation functions show dramatic diŒerence in short-time behaviour. The integrals of the two correlation functions, however, become identical after a short transient period which is signi® cantly shorter than the rotational relaxation time of the molecule. Both reach the same plateau value in a time period corresponding to this relaxation time. These results provide a convenient guide for the choice of the upper integral time limit in calculating the viscosity by the Green± Kubo formula.
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