Chelation energy


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Just Got Here
Hi,

I am new to NWChem, so maybe this question is a little bit silly. I was trying to calculate the binding energy between Fe(III) and a drug (taking solvation into consideration). I started this at a simple way by putting the iron in the middle of the two oxygen atoms that is going to bind and use DFT to optimize it. However, this seems to take too long. I was hoping to develop an algorithm and use it to scan thousands of compounds.

While when I try to use md to optimize it before DFT calculation, it seems to fail because it cannot handle odd-electron situation.

Here is my code:



start ip90

memory 1000 mb

title ip90

basis
*  library 3-21g
end

charge +3

geometry units angstroms print xyz autosym
 O        7.25381       -3.43914       -0.13621
C 6.51987 -2.29219 -0.38678
C 6.93588 -1.25943 -1.16612
C 8.24831 -1.35335 -1.91564
N 6.15399 -0.08810 -1.33029
C 6.58786 1.07789 -2.10918
C 4.89341 -0.04092 -0.74577
C 4.36301 -0.99801 0.01766
C 5.17043 -2.20130 0.27598
O 4.73169 -3.08296 1.01030
H 8.18567 -3.27684 -0.34213
H 8.16970 -0.92614 -2.91924
H 8.56813 -2.38726 -2.07981
H 9.03576 -0.83028 -1.36433
H 7.65229 1.07409 -2.35595
H 6.41254 1.99985 -1.53643
H 6.01564 1.14267 -3.04100
H 4.32954 0.86594 -0.95200
H 3.38190 -0.93696 0.46636
Fe 5.99275 -3.26105 0.43705
end



dft
 maxiter 20
end

cosmo
 do_cosmo_smd true
solvent water
end


task dft optimize
task dft energy



I appreciate it if anyone has any thoughts that could share with me. Either the solution to this question or better idea to handle this situation.

Thank you,

Yuanqing