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[求助]
VASP引入空穴以及電子的一些問題
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關(guān)于VASP中如何引入空穴和電子論壇上有過討論: http://www.gaoyang168.com/html/201106/3322747.html 但我還是有一些問題: 如果我要研究Au/TiO2 的光催化,那么我需要引入一個空穴和一個電子。如果我只關(guān)心電子,用NELECT來引入電子的話,根據(jù) http://cms.mpi.univie.ac.at/vasp ... LDIPOL_EPSILON.html Total energies from charged slab calculations are hence useless, and can not be used to determine relative energies. 如果是這樣的話,原文為何還能計算能量呢? 如果我希望引入的電子停留在Au上的話,有什么辦法呢? 謝謝! |
Photochemistry |
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非常感謝回復~~ 不知道是否可以這么認為:可以通過charged slab 來引入hole,但是這樣計算出來的能量是不對的,需要correction? 如果是這樣的話,那之前提到的那篇算co2- 在tio2上,并沒有correction,是不是認為這樣計算得到的結(jié)果不準確呢? J. Phys. Chem. C 2010, 114, 21474–21481 在VASP 的FAQ里有這樣一段: Q:I adsorb, an ionic species e.g. O$ ^-$ on an insulating surface. To select a specific charge state, I have increased the number of electrons by one compared to the neutral system. Now, I have no clue how to evalute the total energy properly (i.e. are there convergence corrections). A:Actually, you MUST NOT set the number of electrons manually for a slab calculation. I.e., when you calculate the slab-O$ ^-$ system you are not allowed to select a specific charge state for the oxygen ion, by increasing the number of electrons manually. Specific charge state calculations make sense only in 3D systems and for cluster calculations. If you conduct the calculations properly, i.e. if your slab is large enough and the lateral dimension (x,y) of your surface is large enough the energy should converge to the proper value, i.e. the O should acquire the correct charge state automatically. Reason: If you set the number of electrons in the INCAR file for a slab calculation you end up with a charged slab. The electrostatic energy of such a slab is however only conditionally convergent and worse, in practice, even infinite (BASIC, BASIC ELECTROSTATICS). Therefore, no method whatsoever exists to correct the error in the electrostatic energy. E.g. the energy converges towards infinity, when the vacuum width is increased. You can try to validate this, by simply increasing the vacuum width in VASP for a charged slab. You will find that the energy increases or decreases linearly with the vacuum width. Well, there is maybe one method that can surmount the aforementioned problem. You can charge the slab and increase systematically the distance between the O- species (by increasing the lateral dimensions of your supercell) at a fixed vacuum width, and finally extrapolate the energies towards infinite lateral distances. The energy should converge towards the correct value as 1/$ d$, where $ d$ is the distance between the adsorbed species. This might yield a converged value. The point is that, as I mentioned above, the electrostatic energy is only conditionally convergent for the case of a charged slab/system, and results depend on how you evaluate the limit towards infinity. However, to the best of my knowledge, this has not been done or attempted hereto (and therefore we can not assist you on that issue). 這樣的話,如果我只是要計算Au/TiO2 中的charge transfer應該可以,但是如果在光催化下,還有什么方法可以加入electron 和hole 呢? 謝謝! |
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只是說vasp里面沒有方法修正能量charged slab得能量 有些其他方法可以的 但是都比較難弄 需要比較好的理論和編程基礎(chǔ) 樓主可以看看這兩片文章: PRL 102 016402 PRL 110 095505 尤其第二篇講了表面的電荷修正 還有一種方法就是用cluster model 沒有周期性邊界條件的 所以可以隨便加charge 但是vasp做不了 像FHI-aims bigdft之類的可以 用cluster model的問題就是邊界上的原子的性質(zhì)和表面上的是不一樣的 也會造成很多問題 |
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不是那么容易做的 比如說可以引入一個堿金屬 因為電負性很低 所以electron很容易出來 總體系還是保持中性的 (hole的話可以引入一個Cl?)不過這樣做也會引入其他的問題 而且電子的transfer到什么地方怎么就能保證和實際體系一樣呢? 不過倒是可以試一試 這個總的來說是很難做的 哈哈 可能也又其他方法吧 再查查文獻吧! 我看到有人就只做一個au cluster 加電子 你說的那篇jpcc 我沒看 但是如果就加個電子就說自己是有CO2-的話 而且是周期性便捷條件 應該是不對的 沒看過 不知道到底是什么 |
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