8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P8.44Thu 811:10-14:00From ”isomorphs” to a new equation of state forgeneralized Lennard-Jones liquidsThomas B. Schrøder, 1 Nicoletta Gnan, 1 Ulf R. Pedersen, 1 Nicholas P. Bailey, 1 andJeppe C. Dyre 11 Roskilde University, Universitetsvej 1, 4000, Roskilde, DenmarkThe theory of isomorphs in liquids is derived [1] from a single assumption: Two state points(ρ 1 , T 1 ) and (ρ 2 , T 2 ) are defined to belong to the same isomorph if they obey the following: Anytwo physically relevant configurations (r (1)1 , ...,r (1)N ) and (r (2)1 , ...,r (2)N ) that trivially scale into oneanother,have proportional configurational Boltzmann weights:ρ 1/31 r (1)i = ρ 1/32 r (2)i (i = 1, ...N), (1)e −U(r(1) 1 ,...,r(1) N )/k BT 1= C 12 e −U(r(2) 1 ,...,r(2) N )/k BT 2. (2)Only IPL liquids have exact isomorphs, but it can be shown [1] that “strongly correlating liquids”(with strong correlations between potential energy U(t) and virial W(t) in NVT simulations[2]) to a good approximation have isomorphs. From Eq. (2) a number of properties can bederived, e. g. , the excess entropy S ex and heat capacity CVex are invariant on an isomorph.Both structure and dynamics are isomorphic invariant in ”reduced” units. For multi-componentgeneralized Lennard-Jones (LJ) systems further properties can be derived [3]. The predicted shapeof isomorphs in the WU phase diagram is in excellent agreement with simulations. Building onthe isomorph theory, a new equation of state is derived for generalized LJ systems and shown tobe in good agreement with simulations.[1] N. Gnan, T. B. Schrøder, U. R. Pedersen, N. P. Bailey, and J. C. Dyre, J. Chem. Phys.131, 234504 (2009).[2] U. R. Pedersen, N. P. Bailey, T. B. Schrøder, and J. C. Dyre, Phys. Rev. Lett. 100, 015701(2008).[3] T. B. Schrøder, N. Gnan, U. R. Pedersen, N. P. Bailey, and J. C. Dyre, Phys. J. Chem. Phys.134, 164505 (2011).44