[Wien] how

[Saeid Jalali]

Dear Akram,
Basically DFT calculations are performed in the coldest temperature (T=0K).
However, it is not so hard to go beyond this restricted condition (T=0 K)
employing relevant equations of state. To do this one must first find proper
state variables, which are exact differentials, and then try to drive an
equation of state among those state variables using the mathematical
theorems of exact differentials. For example if you would obtain unit cell
volume at T<>0, you can use the following thermodynamical equation of state:
V(T)=V(T=0)*(1 + alpha_P*T - kapa_T*P)
, where V(T=0) is the calculated unit cell volume within DFT at T=0 K,
alpha_P is coefficient of thermal expansion at constant pressure P, kapa_T
is isothermal compressibility at constant temperature T, and T and P are
your desired temperature, and pressure.
For solids there are many equations of state in thermodynamics, but we must
first know what we are looking for. What we are looking for means what
physics we would carry out. It is not so hard to make a big mistake choosing
an equation of state which is not matched to our physics.
Your,
Saeid.

----- Original Message -----
From: "akram hashim" <shahad246 at yahoo.com>
To: <wien at zeus.theochem.tuwien.ac.at>
Sent: Friday, February 13, 2004 8:20 AM
Subject: [Wien] how


> Dear Sir
>    Please I want to ask you if we can do some
> temperature dependency calculations on the band
> structure? and How in case if the answer is yes?
>
>
>     Akram
>
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