When we build a pseudopotential (psp), we froze the inner core states and treat 
only the valence electrons due to the fact that the properties of materials are 
largely determined by the outer-layer valence electrons. In order to obtain a 
psp with good transferability, there should be very small overlap between core 
and valence electron distributions which is true for most light elements. For 
most the elements, the overlap between core and valence electron can be so 
large that the psp built in the usual way cannot lead to the correct properties 
of materials composed of that element (e.g., Na, K). There are two methods to 
solve the above problem. 1) Nonlinear core correction, we use an artificial 
core charge distribution to replace the real core charge distribution. When 
building psp, we substract the contribution to Vxc and VHartree, which comes 
from the artificial core, and when using the psp, add the corresponding ones 
(see PRB 26, 1378). When doing nonlinear core correction, we don't increase the 
number of valence electrons but only increase the cutoff energy for plane-wave 
calculations due to the added core.  2) Semicore states, which means including 
some states that you usually treat as core states when you build a 
pseudopotential. For example, when building a psp for Ca, we not only include 
4s, 4p, 3d but also include 3s, 3p in the valence states. For this method, we 
include a lot more electrons (e.g. 8 more e/atom for Ca), and also need a much 
large cutoff energy because we have included much more localized 3s, 3p 
electrons. So including semicore states will result in much harder 

In fact, for most cases, nonlinear core correction is already enough for a good 
psp and including semicore states is kind of overkill. So my suggestion is: use 
the nonlinear core correction when you need it, use semicore states unless you 
have to. 


----- Original Message ----- 
  From: daijianhong001 
  To: SIESTA-L@listserv.uam.es 
  Sent: Monday, July 13, 2009 2:42 AM
  Subject: [SIESTA-L] semicore state meaning

  Dear all,
  Some pseudopotential includes semicore state.I wonder what is the meaning of 
semicore state and which element includes semicore state?
  Best wishes!


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