C8863 Free Energy Calculations -1-
4. Statistical Thermodynamics – Ideal Gas
Petr Kulhánek
kulhanek@chemi.muni.cz
NCBR - National Centre for Biomolecular Research
&
CEITEC - Central Institute of Technology,
Masaryk University,
Kamenice 5, 625 00 Brno
C8862
Free Energy Calculations
exercise
C8863 Free Energy Calculations -2Excercise
I
1. Determine composition of equimolar mixture of H20 and D2O (in gas or liquid state).
At this time, assume that O-H and O-D bonds have the same energy.
Result: H2O:D2O:HDO=1:1:2
2. How the composition changes if you consider difference between O-H and O-D bonds
(evaluate at qualitative level).
C8863 Free Energy Calculations -3Exercise
II
1. Calculate standard changes of thermodynamic properties such as H, S, and G
describing dimerization of acetic acid in gas phase (ideal gas model) at standard
conditions. Compare DG with the change of potential energy. What is the
contribution of ZPE from vibrations?
Notes:
• all calculations will be done in Gaussian
• first, calculate all data at semiempirical level of theory (PM6)
• if all is OK, then use higher level of theory such as PBE0/def2-TZVPP with D3BJ
dispersion correction (start from geometries optimized on PM6)