Hello,
I'm using Gaussian 09 to try and calculate the adiabatic electron affinity (AEA) of H3PO4. I've done this by running a geometry optimizations and frequency calculations of both H3PO4 (neutral) and H3PO4- (anion), after which I try to calculate the AEA by
AEA = E_neutral - E_anion.
where E is the electronic energy + non-electrostatic effects. Regardless of whether I include zero point corrections etc, I get on the order of 7eV.
However, in the paper "A model of single-electron transport. Calculation of the thermodynamic parameters for electron capture by the bound proton of oxyacids" they claim to calculate an AEA of 1.7eV, which is off by quite a lot compared to mine.
Am I doing the calculation of EA wrong in some way? The paper states that they calculate EA using "calculated as the sum of the total energy of interaction of the electrons and nuclei, energy of formation of the solvation cavity (for the aquatic environment), and zero-point energy"; still, doing that I consistently get on the order of 7eV, regardless of molecule conformation.
I know that in the paper they use Gaussion 03, whereas I use 09, but that shouldn't make that much of a difference. My input routes look like this:
#P UMP2/6-311++G(d,p) SCF=(XQC,MaxCycle=512,NoVarAcc)
OPT=(MaxCycles=999)
IOp(1/6=999,1/152=999) Test
Int(SuperFineGrid) CPHF=SuperFineGrid
SCRF(SMD,Solvent=Water)
Freq FormCheck
Can anyone help me figure out how there's such a large discrepancy between my results and the ones in the paper?
Hi Mathias,
did you try any other method, for example, any DFT functional, for your calculations? I'm afraid the reason for such huge discrepancy could be in using MP2.
Best regards,
Aleksey.
Finding a correct electron affinity by computational methods is a challenging problem. Different methods and also basis sets give significantly different values. You should find a proper method which has been successfully fitted by experimental data.
Dear Mathias,
For electron affinity the equation to be used is:
AEA = E_neutral - E_anion radical and NOT AEA = E_neutral - E_anion.
This makes a lot of difference.
The G03 and G09 are comparable (no effect is expected).
The basis set will not make this large difference.
In addition, you might consider RHF and UHF (closed and open shell calculations).
Hoping this will be helpful,
Rafik
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