Dear Patrick Batoon,

The best way to do this kind of calculations is:

To run a reaction coordinate for the approach of H towards N. For instance if the distance H----N is 4 Angstrom, to do a reaction coordinate of 0.1 A increment for 25 steps.

The following input file is an example of a reaction coordinate in which the distance C--O2 is changed in 0.1 A increment for 10 steps. The angle OCO3 was kept constant. If you want to do a reaction coordinate where all parameters are fixed you should include those parameters under constants as shown for OCO3.

%chk=Formaldehde With OH- RC

   # B3LYP/6-311+G(d,p)Opt=(Z-matrix,MaxCycle=300,CalcFC) GFINPUT IOP(6/7=3)

    RECATION COORDINATE FOR

     -1  1

 o

 c   1 co2    

 o    2 oc3         1 oco3     

 h    2 hc4         1 hco4          3 dih4  

 h    2 hc5         1 hco5          4 dih5  

 h    1 ho6         2 hoc6          3 dih6  

variables:

co2         2.845270 s 10 -0.1

oc3         1.220244

hc4         1.129261

hco4        115.022

dih4        179.992

hc5         1.138643

hco5          1.800

dih5        179.853

ho6         0.963673

hoc6        126.825

dih6         -0.019

constants:

oco3        107.000

Hoping this will be helpful,

Rafik

Mr Batoon,

Please pay attention to a discussion:

https://www.researchgate.net/post/How_to_fix_the_direction_of_atoms_in_Gaussian

 Hi Dr. Rafik,

Thanks you for the information. I have been playing around with your input text for formaldehyde. The matrix system is starting to make more sense to me now, however I cannot open this in GaussView to fully understand which atoms I am looking at. Is it a possibility you can attach a file (.com, .gjf,.txt) that is fully formatted and ready to go for submission?

And thank you Dr. Ivanova,

The discussion you attached is certainly helpful but not useful to the problem I am trying to solve. It is however, very useful in the future if I ever need to optimize these proton bound dimers - which I will eventually.

Dear Patrick,

Attached is the requested file.

Rafik

Are you sure that the diamine geometry is correct? I think that the lowest enegy form must have an internal H-bond. If this diamine form is the proton acceptor, the proton should approach from the side of the nitrogen which give its H atom to the other N.