2ND, 3RD AND CORRELATION MOMENTS FROM NONEQUILIBRIUM AND EQUILIBRIUM FLUCTUATION THEORY, N, P, T ENSEMBLE, COMPARED BETWEEN SUPERCOOLED ANDSUPERHEATED LIQUID WATER

A local nonequilibrium fluctuation (NEF) theory has been developed whi ch applies to modest deviations from equilibrium when gradients, time dependences, etc., are absent, and, provided that long-range spatial c orrelations of the fluctuations are suppressed, for example, by drople t sizes down to 3 mum required to obtain thermodynamic data at the ext remes of supercooling. The predictions from NEF theory are contrasted against those from equilibrium fluctuation (EF) theory using the exten sive data available for metastable liquid water. NEF and EF second and third T and P moments were calculated and compared between the maximu m supercooling and superheating spinodals, almost-equal-to 227 K and a lmost-equal-to 596 K, at 1 atm pressure. The EF second and third T and P moments are either small or zero near 227 K, but [(deltaT)2] and [( deltaP)2] approach + infinity near 227 K, and [(deltaT)3] and [(deltat P)3] approach - infinity and + infinity, respectively, when calculated by NEF theory. Moreover, all NEF second moments, G, A, H, E, P, V, T and S, approach + infinity for supercooled water near 227 K, and corre lation moments, e.g., entropy-pressure, also diverge. The positive inf inities in [(deltaP)2] and [(deltaP)3] require some pressure fluctuati ons to reach the negative-pressure stability limit of supercooled wate r at 227 K, thus causing mechanical instability, but mechanical instab ility at 227 K is not obtained from EF theory. An even more important result is that the NEF second S moment diverges much faster near 227 K then the EF second S moment. This occurs because the NEF second S mom ent contains two diverging terms; the first is the same as the EF seco nd S moment, but the second, more-rapidly diverging term, is related t o the nonequilibrium entropy production. The NEF second E moment also is somewhat larger than the EF second E moment near 227 K, whereas oth er second moments, of A, H and V, are identical in EF and NEF theory. Several NEF second moment divergences do not result just from the infi nities in the individual susceptibilities, but rather from the product of C(P), beta, or K(T), with 1/(C(V)K(T) + betaV), which also approac hes large values near 227 K. Differences between NEF and EF results al so occur up to 596 K for superheated water.