Binding Energy

[rahulprajesh]

Hello Everone,
                  Can anybody please help me finding Binding Energy through this software.Suppose we have a ch3oh molecule then how much energy will be needed to break oh from ch3oh(Meoh).
Thanks ...

[zh]

If the chemical reaction looks like "A+B---->C", the binding energy of C would be estimated by the following way:
Binding energy of C = Total energy of C  -  (Total energy of A + Total energy of C).
So one should separately perform the total energy calculations for A, B, and C.

i) optimize the structure of CH3OH molecule and then calculate its total energy of the optimized CH3OH molecule, [tex]E_{tot}[/tex](CH3OH);
ii) optimize the structure of CH3OH(MeOH) and then calculate its total energy, [tex]E_{tot}[/tex](CH3OH(MeOH));
iii) optimize the structure of OH and then calculate its total energy, [tex]E_{tot}[/tex](OH).
[tex]E_b[/tex](CH3OH(MeOH))= [tex]E_{tot}[/tex](CH3OH(MeOH)) - [tex]E_{tot}[/tex](CH3OH) -[tex]E_{tot}[/tex](OH).

[rahulprajesh]

Thank you Sir,thanks for the  reply but its not working would you please give me any example so that can i can verify My calculation because my calculations are not satisfying the standard values.
 waiting for the reply ..

[zh]

The outlined procedure to calculate the binding energy is rather clear, it is no necessary to provide the example script files to demonstrate this procedure.

The discrepancy between the theoretical and experimental values may be due to the following possible reason:
the LDA usually overestimates the binding energy, while the GGA usually underestimates the binding energy.


 

[rahulprajesh]

okay sir,    but sir  by gga or by Lda i calculated the the binding energy of CH4 for molecule it's quite diffrent from its standard value. i used the procedure:
(4*Tot_Energy_of H + Total_energy_of C) - (Total_Energy_of Ch4) = 25.121eV     (by GGA.pbe )
but the Standard value is approx = 17.25 eV..
What should I do ??
i've also tried for Single bond energy of C-H in the same way it comes out to be = 7.3082 eV(but Std.=4.5eV )

                    Help me Sir...Thanks

[Anders Blom]

I suggest you compare your approach with that posted in http://quantumwise.com/forum/index.php?topic=22.msg54#msg54 for methane (CH4).

Note that that post deals with atomization energy, however, so some modifications are needed for binding energies of larger fragments.

[zh]

okay sir,    but sir  by gga or by Lda i calculated the the binding energy of CH4 for molecule it's quite diffrent from its standard value. i used the procedure:
(4*Tot_Energy_of H + Total_energy_of C) - (Total_Energy_of Ch4) = 25.121eV     (by GGA.pbe )
but the Standard value is approx = 17.25 eV..
What should I do ??
i've also tried for Single bond energy of C-H in the same way it comes out to be = 7.3082 eV(but Std.=4.5eV )

                    Help me Sir...Thanks

Which basis set is used in your calculations? To get accurate results, one had better adopt the DZP basis set at least. In addition, the geometry of CH4 molecule should be well optimized.