[Wien] excited state of a system

[shamik chakrabarti]

Dear Stefaan Sir,

 Thank you very much for clearing all of my
doubtsThank you very much Sir.

with best regards,

Shamik Chakrabarti

On Thu, May 6, 2010 at 4:34 PM, Stefaan Cottenier <
Stefaan.Cottenier at ugent.be> wrote:

>
> > But is your reply indicating that...
>
>>
>> the excited states *may be* those states having higher energybut it is
>> *not sure* that whether the states having higher energy will be the excited
>> states of the system??..Please assure me that this is the meaning of
>> your reply...
>>
>
> Yes.
>
>
>  but if this is the meaning then another question is that may it be
>> happened that some converged solutions of the system actually never be found
>> in reality??...
>>
>
> Sure. You examined only ferromagnetic, antiferromagnetic and 'non-magnetic'
> states. But for sure there are many more magnetic configurations for which
> you can get a converged solution. And the same holds also for the structural
> degrees of freedom: you will find converged solutions for your solid in e.g.
> bcc, fcc, ... crystal structures. No way to find all these many situations
> if you increase the temperature.
>
>
>  if this is true then the question is why?
>>
>
> Many possible reasons:
>
> * all calculated information is at 0 K. Phonons and all kinds of electronic
> excitations will enter the game at temperatures above 0 K, and these might
> alter the picture.
> * something else might have happened before (e.g. a structural phase
> transition occurs before you reach the point where a magnetic phase
> transition in the original material would have occurred)
> * some solutions correspond to saddlepoints, and will spontaneously evolve
> to another solution
> * your material might be molten before you reach the energy corresponding
> to a particular case
> *...
>
>
> Stefaan
>
> ___
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>



-- 
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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[Wien] excited state of a system

[shamik chakrabarti]

Dear Stefaan Sir,

 Thank you for your reply. But is your reply
indicating that...

the excited states *may be* those states having higher energybut it is *not
sure* that whether the states having higher energy will be the excited
states of the system??..Please assure me that this is the meaning of
your reply...but if this is the meaning then another question is
that may it be happened that some converged solutions of the system actually
never be found in reality??...if this is true then the question is
why?..Please forgive me to ask so many questions at a time.

with best regards,

Shamik Chakrabarti

On Thu, May 6, 2010 at 3:57 PM, Stefaan Cottenier <
Stefaan.Cottenier at ugent.be> wrote:

>
> I have a basic question regarding DFT. Say for
>> some system we calculate antiferromagnetic, ferromagnetic and non spin
>> polarized state and by comparing energy we find that the antiferromagnetic
>> state is the ground state. Now as ferromagnetic and non spin polarized
>> states are also two converged solutions of the system can we consider them
>> as some excited states which can be found at higher temperature (other than
>>  0K).??
>>
>
> Yes. But the important word is: "which CAN be found". This is not "WILL be
> found".
>
> Stefaan
>
> ___
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>



-- 
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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[Wien] excited state of a system

[shamik chakrabarti]

Dear wien2k users,

I have a basic question regarding DFT. Say for
some system we calculate antiferromagnetic, ferromagnetic and non spin
polarized state and by comparing energy we find that the antiferromagnetic
state is the ground state. Now as ferromagnetic and non spin polarized
states are also two converged solutions of the system can we consider them
as some excited states which can be found at higher temperature (other than
 0K).??...Any response will be of great help for our understanding.
Thanks in advance.

with regards,

-- 
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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[Wien] excited state of a system

[Stefaan Cottenier]

 > But is your reply indicating that...
> 
> the excited states *may be* those states having higher energybut it 
> is *not sure* that whether the states having higher energy will be the 
> excited states of the system??..Please assure me that this is the 
> meaning of your reply...

Yes.

> but if this is the meaning then another 
> question is that may it be happened that some converged solutions of the 
> system actually never be found in reality??...

Sure. You examined only ferromagnetic, antiferromagnetic and 
'non-magnetic' states. But for sure there are many more magnetic 
configurations for which you can get a converged solution. And the same 
holds also for the structural degrees of freedom: you will find 
converged solutions for your solid in e.g. bcc, fcc, ... crystal 
structures. No way to find all these many situations if you increase the 
temperature.

> if this is true then the question is why?

Many possible reasons:

* all calculated information is at 0 K. Phonons and all kinds of 
electronic excitations will enter the game at temperatures above 0 K, 
and these might alter the picture.
* something else might have happened before (e.g. a structural phase 
transition occurs before you reach the point where a magnetic phase 
transition in the original material would have occurred)
* some solutions correspond to saddlepoints, and will spontaneously 
evolve to another solution
* your material might be molten before you reach the energy 
corresponding to a particular case
*...

Stefaan

[Wien] excited state of a system

[Stefaan Cottenier]

> I have a basic question regarding DFT. Say 
> for some system we calculate antiferromagnetic, ferromagnetic and non 
> spin polarized state and by comparing energy we find that the 
> antiferromagnetic state is the ground state. Now as ferromagnetic and 
> non spin polarized states are also two converged solutions of the system 
> can we consider them as some excited states which can be found at higher 
> temperature (other than  0K).??

Yes. But the important word is: "which CAN be found". This is not "WILL 
be found".

Stefaan