[QE-users] 回复: Is it acceptable to neglect spin, magnetism and U for CPMD simulation of iron oxides (Fe2O3, Fe3O4 and FeO)

[likejiang at ustb.edu.cn]

Dear Giuseppe,

Thanks a lot for your prompt response and sharing your experience.

Yes, I found that there are parameters (nspin, tot_magnetization,
lda_plus_u, Hubbard_U(i)) that can be used to set spin, magnetism and U in
cp.x. But after I set these parameters (nspin = 2 , tot_magnetization=0,
lda_plus_u = .TRUE, hubbard_u(1) = 4.2), I found that it will be more
difficult for the iron oxide system to converge in the electronic
minimization and ionic minimization process. This might be due to the
unproper setting of other parameters or selection of pseudopotentials.

Anyway, I will do more tests considering spin, magnetism and U with
different pseudopotentials. I will let you know if any progress or problem.

Thanks again.

All the best,
Kejiang


-----邮件原件-----
发件人: users-bounces at lists.quantum-espresso.org
<users-bounces at lists.quantum-espresso.org> 代表 Giuseppe Mattioli
发送时间: 2022年4月7日 18:39
收件人: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
主题: Re: [QE-users] Is it acceptable to neglect spin, magnetism and U for
CPMD simulation of iron oxides (Fe2O3, Fe3O4 and FeO)


Dear Kejiang

Only EXX functionals such as PBE0 or HSE significantly increase the
computation time. DFT+U has been primarily developed as a cost-effective
method to correct delocalization errors in the case of localized shells such
as those present in transition metal oxides.  
There are tons of literature on this... In my opinion (and I've investigated
several similar system with the same purpose) you cannot neglect U, spin&co
if you want to obtain meaningful (i.e.,
publishable...) results. cp.x can manage open shell systems with a fixed
magnetic moment within the DFT+U framework. But you must carefully setup and
test your calculations, which are a bit on the "nonstandard" side.
HTH
Giuseppe

Quoting likejiang at ustb.edu.cn:

> Dear QE-Users,
>
> I am planning to do some CPMD simulation about iron oxides (Fe2O3, 
> Fe3O4 and
> FeO) and their reactions with hydrogen at high temperature using cp.x 
> of QE 7.0.
>
> As it is well known that spin and magnetism are the most fundamental 
> characteristics for iron and its oxides, we should consider them (spin 
> and
> magnetism) and add U in many cases for 'scf' or 'relax'/'vc-relax'
> calculations with pw.x.  But it seems that considering spin, magnetism 
> and U will make things more complicated and significantly increase the 
> computation time, I am wondering whether it is acceptable to neglect 
> spin, magnetism and U for CPMD simulation of iron oxides (Fe2O3, Fe3O4 
> and FeO) and their reactions with Hydrogen gas. My goal is only to try 
> to simulation the reduction process in atomistic scale, and the CPMD 
> trajectory results are sufficient to capture the reduction mechanism 
> while the accuracy of band gap, magnetism is not the focus of my study.
>
> Any comments or suggestions will be much appreciated.
>
> Thanks,
> Kejiang
>
> -------------------------------------------------
> Dr. Kejiang Li
> School of Metallurgical and Ecological Engineering, University of 
> Science and Technology Beijing Xueyuan Rd., Haidian District, Beijing 
> 100083, P. R. China https://kejiangli.com/



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>

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