Loss of Translational entropy calculation in FEP

From: Daniel Torrente (xlb608_at_my.utsa.edu)
Date: Wed Jul 30 2014 - 16:57:08 CDT

Dear all,

Reading the FEP tutotial in the "Binding of a potassium ion to 18-crown-6"
section they measure the the loss of translational entropy using:

−1/βln(c0∆v), where

β is equal to kB (0.001987 kcal/mol/K) * T (300 K), c0 is the standard
concentration of the ion (1mol /L=1660.6 cubic angstroms per molecule) and
∆v is the volume sampled of the ion (0.53 cubic angstroms).

In the tutorial the loss of entropy was equal to 4.8 kcal/mol but using
those values does not give me the same result. Am I overlooking an
important thing on the formula?. The standard concentration value was take
it from this post (
I also checked other units for the c0 (mol/L) and ∆v (L) and the value of
the loss entropy is not even close.

Truly sorry for asking this type of question here.


University of Texas at San Antonio

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