Thanks for your
I am summarizing the
I have three composition.
I would like to understand
which structures are stable and hence
decided to calculate formation (or Cohesive)
Lets take the first two cases and
calculate Formation energy by the below
Formation Energy of 1 (E1) = Total energy of
A1-B3-C4 -(Energy of 1*A + Energy of 3*B + Energy of 4*C).
Formation Energy of 1 (E2) = Total energy of
A2-B4-C5 -(Energy of 2*A + Energy of 4*B + Energy of 5*C).
Does the direct comparison (E1, E2) makes
Can i conclude if E1>E2, then composition 1 is
I feel, i am missing something.
Your help would be appreciable.
I would say
that your approach is valid, under the condition that the A, B, and C
sensible moieties. It reminds a bit of
However, I would say that if E1 > E2 (e.g. +2
vs. -10) that 2 is more stable, not 1.
Dr Marcel Swart, FRSC
ICREA Research Professor at
Química Computacional i Catàlisi (IQCC)
COST Action CM1305 (ECOSTBio) chair
Girona Seminar 2016
Young Academy of Europe (Board)
the concept of stability is not that straightforward. Thermodynamics does not
provide the final answer. The stability of a molecule not only depends on its
formation energy, but it depends also on the relative energies of its
neighboring local minima on its potential energy surface and the energy barrier
between the minimum and its immediate neighboring minima (kinetic stability). To
begin, I would rather check the depth of minimum energy well by looking at
frequencies. In the next step ab initio/MC/DFT- MD simulations can provide more
insight toward the kinetic stability. Then of course we can define stability
with respect to a particular reaction. Is your molecule stable when it is in the
presence of air/water/light/etc.
be more precise about stability.
I hope my
general answer can help you to solve your problem.
Cina Foroutan-Nejad, PhD
CEITEC-Central European Institute of
Kamenice 5/A4, Masaryk University, Brno,
am not exactly certain what you want to do but if you want to estimate is
composition A1-B3-C4 is more stable than A2-B4-C5, you should calculate the
energy of this "reaction" ...
A1-B3-C4 + A + B + C
you have a mass balanced equation. Assuming the energies of these components are
negative, then if E(Right Hand Side) - E(Left Hand Side) is negative the
LHS is more stable. This means A2-B4-C5 as a compound is more stable
than A1-B3-C4 and an extra A, B, and C.
Thanks and best regards,