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Perhaps I should have mentioned earlier that I am using a precompiled Windows executable of nwchem 6.0. The cube files are similar but they should be identical to several decimal digits, not just the first, which makes me wonder whether the dplot command prints the scf density instead of the MP2 density in the final cube file. The freeze core / freeze atomic keywords don't seem to affect the result. If everything agrees closely except the final cube, that would be surprising. The earliest significant numerical divergence between the two jobs needs to be corrected or explained before downstream results. You would think that the definition of '6-31G**' was set in stone long ago, but I have been surprised in the past to find how software has interpreted named Pople basis sets. Are the numbers of orbitals and basis functions the same for both calculations? Do the energies for SCF and MP2 agree to a reasonable number of decimal places? You may also want to manually compare the basis set definitions that are echoed in the output files. If the results still don't match it is time to carefully read your Firefly and NWChem output files side by side.

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I read the Gaussian manual about frozen cores and there sure are a lot of options! I don't know if NWChem's 'freeze atomic' is equivalent to the default Gaussian freezing scheme for post-HF calculations, but it's worth a quick try.

This doesn't actually do anything - you need to put a greater-than-zero number after 'core' for it to have an effect, e.g. GAMESS-US and Firefly have diverged more than I thought.ДЄfter some reading and looking I noticed your 'freeze core' directive. Geometry units angstroms print xyz nocenter noautosym O 0.00000 0.00000 0.00000 Is there something wrong with the syntax or is it just a matter of different numerical precision/approximations? I have been able to reproduce the exact same result in pcgamess/firefly, but I have no experience with nwchem. I have tried the following syntax, but the density is slightly different to the original gaussian cube's (while the grid's dimensions are identical).

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I do not own a gaussian license, therefore I am trying to reproduce this particular calculation using free software. More specifically, I am trying to reproduce the results of the following Gaussian input file: I am trying to output the MP2 density in gaussian cube file format.

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