Dear student,

H = U + PV
G = A + PV

In differential form we have

dH = dU + PdV + VdP = TdS + VdP
dG = dA + PdV + VdP = -SdT + VdP

Free energy functions are  at the heart of chemical thermodynamics. They describe the spontaneous  direction for a process in terms of the heat released by a reaction (DH) and the entropy change in the system (DS).  If the heat exchanged with the surroundings creates a greater disorder  in the surroundings than the order in the system created during the  process, then it will be spontaneous. Understanding free energy is  important in the context of molecular dynamics simulations. The  potential energy surface defined by the individual terms (i.e. bond  stretching, angle bending, torsions, and van der Waals) gives the  contribution to the internal energy, but does not say anything about the  entropy. The entropy is proportional to the number of states accessible  to the system, and by the ergodic hypothesis that can be sampled by  allowing a simulation to run for an infinitely long period of time and  counting the states. Thus, our estimate of the entropy will be the  weakest aspect of a computer simulation.
 








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US20080014252A1




H = U + PV
G = A + PV

In differential form we have

dH = dU + PdV + VdP = TdS + VdP
dG = dA + PdV + VdP = -SdT + VdP

Free energy functions are  at the heart of chemical thermodynamics. They describe the spontaneous  direction for a process in terms of the heat released by a reaction (DH) and the entropy change in the system (DS).  If the heat exchanged with the surroundings creates a greater disorder  in the surroundings than the order in the system created during the  process, then it will be spontaneous. Understanding free energy is  important in the context of molecular dynamics simulations. The  potential energy surface defined by the individual terms (i.e. bond  stretching, angle bending, torsions, and van der Waals) gives the  contribution to the internal energy, but does not say anything about the  entropy. The entropy is proportional to the number of states accessible  to the system, and by the ergodic hypothesis that can be sampled by  allowing a simulation to run for an infinitely long period of time and  counting the states. Thus, our estimate of the entropy will be the  weakest aspect of a computer simulation.