null bader charges
Posted: Wed May 15, 2013 10:36 am
dear all,
i'm new to this software, and i've some very weird results, i wonder if someone could throw some hints my way...
i optimized some molecules using nwchem, and generated a gaussian-format cube file using nwchem dplot function, and then computed bader charges from those cube files. major issue is:
nwchem dplot requires me to specifity limit x,y,z values and grid spacing values to generate the cube file. at first i just asked for 100x100x100 points between (-10,-10,-10) and (10,10,10) [all the molecules are within that region] and i got some nasty results, like carbon atoms [in organic compounds] with -4 partial harge [after subtracting the computed charge from the electrons of C].
then i choose much narrower regions in nwchem, just enough to include the molecule plus 1 angstrom on each side, and I got much more realistic charges BUT ACF.dat will then give me bader charges of 0.000 for some C atoms which lead to irrealistic partial charges.
note: the "bad" C atoms in the 1st case are "ok" in the 2nd case, and the "bad" C atoms in the 2nd case were "ok" in the 1st case.
in the former case i get around 139 electrons, in the latter around 108, if that matters
using the nwchem computed charges, i get reasonable partial charges - they tend to go a bit akward in some atoms, thus i went on to try new approaches to compute partial charges...
so, any hints on how these nasty partial charges arise ?
i understand different volumes lead to different charge distributions (well, it's the core of bader charge analysis), but how can that lead to such marked differences in the charge of a couple of specific atoms ?
any ideas on how to bypass this ?
thanks in advance,
all the best,
e.
i'm new to this software, and i've some very weird results, i wonder if someone could throw some hints my way...
i optimized some molecules using nwchem, and generated a gaussian-format cube file using nwchem dplot function, and then computed bader charges from those cube files. major issue is:
nwchem dplot requires me to specifity limit x,y,z values and grid spacing values to generate the cube file. at first i just asked for 100x100x100 points between (-10,-10,-10) and (10,10,10) [all the molecules are within that region] and i got some nasty results, like carbon atoms [in organic compounds] with -4 partial harge [after subtracting the computed charge from the electrons of C].
then i choose much narrower regions in nwchem, just enough to include the molecule plus 1 angstrom on each side, and I got much more realistic charges BUT ACF.dat will then give me bader charges of 0.000 for some C atoms which lead to irrealistic partial charges.
note: the "bad" C atoms in the 1st case are "ok" in the 2nd case, and the "bad" C atoms in the 2nd case were "ok" in the 1st case.
in the former case i get around 139 electrons, in the latter around 108, if that matters
using the nwchem computed charges, i get reasonable partial charges - they tend to go a bit akward in some atoms, thus i went on to try new approaches to compute partial charges...
so, any hints on how these nasty partial charges arise ?
i understand different volumes lead to different charge distributions (well, it's the core of bader charge analysis), but how can that lead to such marked differences in the charge of a couple of specific atoms ?
any ideas on how to bypass this ?
thanks in advance,
all the best,
e.