Hello,
I need to calculate the difference of the electron density of a dimer and the the sum of its monomers. I tried G09 without success, even using nosymm in all calculations. The problem occurs when I tried to sum the monomer cube files, by using cubman, GaussView or multiwfn. The result cube superposes both monomers. Probably I am missing something.
Any hint?
Thanks,
Sergio
Dear Prof. Galembeck,
In order to do any mathematical operation (such as difference density) on cube files, the grid dimension of all cube files must be the same, otherwise, they will show an error. I think if you use a reference .cube file via cubefile2 option in cubegen (https://gaussian.com/cubegen/) for generating the cube for the monomers, the issue will probably be resolved. In my experience, it is best to take the cube for the dimer as the reference, since it is the largest.
In Multiwfn manual, there is an example of calculating electron density between two monomers and plotting it as isosurface map, see Section 4.5.5. The related Gaussian input files and wavefunction files are all provided, by comparing your calculation with the example files you can easily identify the reason of your problem, all points should be paid attention to have also been mentioned in this manual section. Note that by using Multiwfn, you do not need to generate cube files (like using cubegen+cubman), because Multiwfn is directly able to calculate grid data of electron density based on wavefunctions of dimer and monomers, this makes the calculation and visualization much easier. In addition, Section 4.4.8 of Multiwfn manual also illustrates how to plot this kind of map using water tetramer as instance.
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