Hi,
I am fairly new to molecular modeling so I am trying to do some basic things to validate my thinking. I am trying to test the calculation of the heat of mixing for common mixtures. I am calculating it from cohesive energy densities (CEDs) of the pure components and of mixtures. The pure components come out OK - CED is close to heat of vaporization. Unfortunately, I am coming up with some strange results for the heat of mixing. I cannot even correctly predict the sign of the delta H, much less magnitude!
| Heat of Mixing Test | |||||||||||
| pure components: | Mw | mass frac | mol frac of 1 | density | CED (J/cc) | CED predicted (from deltaHvap) | CED error (%) | ||||
| ethanol | 46 | 1 | 1 | 0.77 | 657 | 662 | 0.007945469 | ||||
| water | 18 | 1 | 1 | 0.95 | 2187 | 2173 | -0.006351462 | ||||
| phenol | 94 | 1 | 1 | 1.05 | 570 | 645.8617021 | 0.116964982 | ||||
| benzoic acid | 122 | 1 | 1 | 1.18 | 793 | 737.1007371 | -0.070490874 | ||||
| mixtures: | mass frac | mol frac of 1 | density | pred. density | CED (J/cc) | CED ideal mix | deltaH/V (J/cc) | deltaH J / mol | Expected deltaH J/mol | ||
| ethanol+water | 0.5 | 0.28125 | 0.83 | 0.850581395 | 1209.177567 | 1309.218701 | 100.0411 | 3201.316 | -660 | ||
| benzoic acid + phenol | 0.5 | 0.435185 | 1.13 | 1.111210762 | 695.79618 | 686.5848216 | -9.21136 | -994.827 | 1000 | ||
Simulation details: Forcite, unit cells are about 100 molecules, ultra-fine simulations, ultra-fine CED calculations. 300K. 200 ps of dynamcs. TP ensemble.
