[Pw_forum] how to build cell for diamagnetic material?

[duchl06]

thanks for everyone's reply, especially Gabriele Sclauzero's detailed explanation.
 
best regards!
 
graduate student: chen
xiaguanying university



在2009-10-02，"Gabriele Sclauzero" <sclauzer at sissa.it> 写道：
>
>
>duchl06 wrote:
>> hi,Gabriele Sclauzero
>> thanks for your advice and hoping your further guide.
>> i am reading a paper "Charge-Transfer-Based Mechanism for 
>> Half-Metallicity and Ferromagnetism in one-Dimensional 
>> OrganometallicSandwich Molecular Wires"
>> http://pubs.acs.org/doi/abs/10.1021/ja804053a
>> in this paper they consider a sandwich molecular wires (such as 1D 
>> (VBz)∞ wire, (MnCp)∞ wire, Bz is benzene, Cp** is cyclopentadienyl), and 
>> they said "Furthermore, we investigate the effect of doubling the unit 
>> cell size along the SMW direction to evaluate the ground state of 
>> ferromagnetic (FM), antiferromagnetic (AFM), and diamagnetic (DM) 
>> configurations in our spin-polarized calculations with structural 
>> optimization,
>
>In this paper, I think they refer to a non-magnetic ground-state as "DM configuration".
>A priori you do not know if the DFT ground state (which does not necessarily always 
>correspond to the true physical GS) will be FM, AFM or non-magnetic. You have to allow the 
>system to "explore" an enlarged phase space with non-zero magnetization and see if the 
>energy of a magnetic configuration (either FM or AFM) is lower than the non-magnetic 
>solution.
>Actually, if the GS is non-magnetic, you should end to the non-magnetic GS even if you 
>start from a magnetic configuration (unless you get trapped in some local minimum).
>I think that's why \Delta E in table 1 of the paper you pointed out is always negative (or 
>not given): if the GS is magnetic, it will have a lower energy than the lowest energy 
>non-magnetic solution, otherwise the GS is not magnetic and a spin-polarized calculation 
>will give the same GS of a non-spin polarized one.
>
>HTH
>
>GS
>
>
>
>> and assess possibility of the Peierls transition."
>>  
>> 
>>   (and i also found in some other papers when they do not know the groud 
>> state is FM or DM, they would always say "To examine the stability of 
>> the local magnetic state, we calculate the energy difference between the 
>> diamagnetic and ferromagnetic states".
>> 
>> 在2009-10-02，"Gabriele Sclauzero" <sclauzer at sissa.it> 写道：
>>>
>>>
>>>duchl06 wrote:
>>>> thanks every one's reply!
>>>> hi, Hui Wang
>>>> the example you supplied is a calculation for a antiferromagnetic 
>>>> material, i mean how to set the start magnetic moment for the 
>>>> diamagnetic material,
>>>
>>>Diamagnetic material in absence of an external magnetic field should have no net magnetic 
>>>moment per atom, if I'm not wrong. So it is not clear to me what do you want to study and 
>>>if all these suggestions are pointing you to the correct solution. If you want to study a 
>>>diamagnetic material in absence of magnetic field there should be no need for a 
>>>spin-polarized calculation.
>>>So, just to agree on the starting point of your question: what you mean with diamagnetic 
>>>material is really what people usually refer to? Can you give us more details on the 
>>>system you want to address? What properties do you want to study? ...
>>>
>>>Regards,
>>>
>>>
>>>GS
>>>
>
>-- 
>
>
>o ------------------------------------------------ o
>| Gabriele Sclauzero, PhD Student                  |
>| c/o:   SISSA & CNR-INFM Democritos,              |
>|        via Beirut 2-4, 34014 Trieste (Italy)     |
>| email: sclauzer at sissa.it                         |
>| phone: +39 040 3787 511                          |
>| skype: gurlonotturno                             |
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