The finite difference thermodynamic integration, tested on calculating the hydration free energy difference between acetone and dimethylamine in water

1987 ◽  
Vol 86 (12) ◽  
pp. 7084-7088 ◽  
Author(s):  
M. Mezei
Keyword(s):  
Free Energy ◽  
Finite Difference ◽  
Energy Difference ◽  
Thermodynamic Integration ◽  
Hydration Free Energy ◽  
Free Energy Difference

Hydrogen bonding solvent effect on the basicity of primary amines CH3NH2, C2H5NH2, and CF3CH2NH2

1981 ◽  
Vol 59 (1) ◽  
pp. 151-155 ◽  
Author(s):  
Yan K. Lau ◽  
P. Kebarle
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Ion Source ◽  
Primary Amines ◽  
Hydration Free Energy ◽  
Ion Hydration ◽  
Free Energy Difference ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Good Agreement

The equilibria RNH3+(H2O)n−1 + H2O = RNH3+(H2O)n were measured for R = CH3, C2H5, and CF3CH2 from n = 1 to n = 3 with a pulsed electron beam high ion source pressure mass spectrometer. The proton and hydrate transfer equilibria CH3NH3+(H2O)n + C2H5NH2 = CH3NH2 + C2H5NH3+(H2O)n were measured for n = 0 to n = 3. These data allow the evaluation of ΔH0 and ΔG0 for the reactions: R0NH3+(H2O)n + RNH3+ = R0NH3+ + RNH3+(H2O)n. ΔH0 = δΔH00,n(RNH3+), ΔG = δΔG00,n(RNH3+). These data are compared with δΔE0,3 (STO-3G) evaluated by Hehre and Taft. In general good agreement is observed at n = 3. The δΔH00,3(RNH3+) ≈ δΔE0,3(RNH3+) are also found close to the ion hydration free energy difference in aqueous solutions.

On the relationship between free energy difference calculations by thermodynamic integration and harmonic frequency analysis

2009 ◽  
Vol 87 (3) ◽  
pp. 496-501
Author(s):  
Jason Jechow ◽  
Tom Ziegler
Keyword(s):  
Free Energy ◽  
Statistical Mechanics ◽  
Frequency Analysis ◽  
Helmholtz Free Energy ◽  
Energy Difference ◽  
Thermodynamic Integration ◽  
Point Of View ◽  
Harmonic Frequency ◽  
Free Energy Difference ◽  
The Relationship

Harmonic frequency analysis (HFA), based on statistical mechanics, is a widely used and powerful tool for evaluating free energy changes between molecular states. It has, as such, been employed extensively to evaluate the free energy of reaction and activation for chemical processes. Alternatively, free energy differences can be calculated using thermodynamic integration (TI). In TI, the force on a constrained reaction coordinate is calculated, and this force from a to b is integrated to obtain the Helmholtz free energy change ΔAab. Although HFA and TI clearly are related from a fundamental statistical mechanics point-of-view, the relationship is not immediately obvious when one considers the quite different procedures applied in the two methods. This article provides a detailed analysis and proof of the relation between HFA and TI.

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