[Pw_forum] Mulliken population

Agostino Migliore amigliore at cmm.upenn.edu
Tue Jan 15 18:02:59 CET 2008

Hello Kesong

The effective charges mentioned in the user-guide are to be considered
within response theory. Moreover, if you want to reason on an atomic
basis, they should correspond to Lowdin charges.

Instead, as stressed by Axel, it is not appropriate and not "directly"
feasible to look at Mulliken population (which already has various
shortcomings by itself, although can be useful for qualitative,
comparative analyses) from data by a plane-wave code. A good possibility
is to exploit the information from the projwfc post-processing. This is
anyway a necessary step if you insist in making a further population
analysis through some home-made program.

If, on the other hand, your aim is to quantify, in some manner, charge
distribution, you can use pp.x.
As a matter of fact, from this post-processing, you can also get the
overall charge distribution which fits the resulting electrostatic
potential (to this aim, anyhow, Mulliken charges should not be good). In
fact, through the option plot_num=11 (in 3.2 version) you can get the
electrostatic potential. Hence, by exploiting Poisson equation, you can
write an easy program to get charge distribution (anyway, never forget
that atomic cores are treated by means of pseudopotentials). The latter
takes rightly into account valence electron distribution. So, it is much
better than any point-charge schemes (like, e.g., resp charges in NWChem).
I hope my information is useful to you

Agostino Migliore

> Hi, everyone
> It is very easy to obtain the Mulliken population of the atom in the
> output file using CASTEP or VASP code.
> I am sorry but i cann't find it in the output file of PWSCF code. Somebody
> can tell me where can i find it?
> Does the "effective charges" mentioned in the users-guide mean the
> Mulliken population?
> Best wishes.
> Kesong Yang
> School of Physics and Microelectronics
> Shandong University, Jinan 250100, People¡¯s Republic of China
> Email: ksyang at mail.sdu.edu.cn;
>        yupiaofei at mail.sdu.edu.cn
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