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the dipole.dat file

Posted: Fri Sep 15, 2006 9:48 pm
by lmiao
I try to calculate the dipole moment of CO. My dipole.dat file is
# X Y Z MAGNITUDE
--------------------------------------------------------------------
1 0.000005 0.000010 4.698947 4.698947
2 0.000004 0.000006 5.309313 5.309313

So, what is the unit of the magnitude? is it electron-A as used by VASP or debye? In this case, is the total dipole moment of CO molecule 4.698947-5.309313=-0.610366? But why it is different from VASP calculations, which give -0.028516 (e-A)?

Posted: Fri Sep 15, 2006 9:59 pm
by graeme
It's good to be very caution with this dipole data. This is a fairly untested part of the code.

The calculated dipoles are in e-A, but they are not directly comparable to the dipole of the molecule (which vasp is reporting) without some extra calculation.

These dipoles are only due to electron displacement from each atomic center. They are calculated as the integral of charge times distance over the Bader volumes at each atom: Int(rho*r). They do not take into account the nuclear charge, or charge transfer between the nuclei. To get the total dipole of the molecule, you need to add in these other components. To do this, you just need the Bader charges, the nuclear charges, and the vector between the C and O atoms.