[Wien] Very elemental questions...

[Rocquefelte]

Dear Gerardo,

It seems that your question need a more general lesson about theoretical 
chemistry of physics and does not strictly concern the Wien2k code.
Let me reorder your questions:
*1- Why the Total Energy for my calculated systems it's negative?
*In very simple terms, the total energy express the benefit the system 
has to be like this (the benefit to be together in such a bonding and 
structure).
The total energy express how much the system is stabilized in terms of 
kinetic and potential energy ... Thus it is a negative number ... In 
other words, lets consider that the energy of vacuum is 0eV, then the 
energy of each states defining the system will be negative, and the sum 
of these energy correspond to the total energy (which is then also 
negative).
Consider the simplest case, an hydrogen atom: the energy of the 1s 
orbital is -13.6 eV. So if you have one electron on this orbital the 
energy of the system will be -13.6 eV ...

*2- How the Exchange-Correlation term is explained??, i mean, these 
terms corresponds to ...?*
Lets consider a system containing 9 electrons, to deduce its properties 
from theory we have to find the wave function and the total energy 
defining this system.
It means that we have to solve* 1 Schrödinger* equation for a system 
containing *9 interacting electrons*

However, the repulsive interaction between electrons cannot be expressed 
exactly and we realized an approximation which is contained in the 
exchange-correlation potential (the interaction can be decomposed in two 
different contribution: exchange and correlation depending of the spin ...).

In practice, we do not solve 1 equation for 9 interacting electrons but 
we* solve 9 equations *of non-interacting electrons which feels the 
interaction from an* effective potential (w*hich contain the 
exchange-correlation potential at least).
*
3- About DOS and band structure ...*
DOS and band structure simply express the distribution of the energy 
levels of the system. Because of the solid effect, the states are not 
all localized and you have a dispersion of the energy levels forming 
bands. These notions are very simply explained in many books and web 
sites. I recommend you to search more carefully these notions before 
doing any Wien2k calculations.

Hope this will help you ...

Regards

Xavier

Gerardo Felix Martinez a écrit :
> Hi dear Wien2k users!!! i'm trying to understand as much as possible 
> how Wien2k works in some specific things, but i can't understand it 
> fully. That's why i'm  asking you for your help answering this questions:
>  
> - How is the DOS calculated by Wien2k?? I mean, how can this process  
> be explained in the simplest way possible.
> - The same question for the Band Structure.
> - How the Exchange-Correlation term is explained??, i mean, these 
> terms corresponds to ...???
> - Why the Total Energy for my calculated systems it's negative???
>  
> I hope you can help me.. Thanks a lot in advance.
> ------------------------------------------------------------------------
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