[Pw_forum] Ewald and Coulomb

[Yunpeng Wang]

what do you mean by "true Coulomb potential"? Based on density functional theory, adding an uniform potential to the system make no difference. In fact, the ion-ion interaction energy is an infinite value because of 1/r type of Coulomb potential. However, if an uniform charge density which makes total charge zero, hence uniform Coulomb potential is added to the system, the electrostatic energy as well as potential is finite, at the same time, physics keep unchanged.
best wishes,Yun-Peng

Date: Fri, 13 Jan 2012 21:49:59 +0800
From: daijiayu at nudt.edu.cn
To: pw_forum at pwscf.org
Subject: [Pw_forum] Ewald and Coulomb


	Dear users and developers,

	

	Happy new year!

	

	I have a confusion about the calculations of ion-ion interactions. We know, we usually use Ewald scheme to represent the real Coulomb potentials in a periodic cell. Generally, it is correct for a neutral system or one electron taken out (or into ) system. However, if the system is constructed with partially charged ions, that is to say, there are more positive charges than negative charges, the Ewald scheme should be not right. Although this system is not stable, but there should be some properties deserved to study.

	

	So, how can we calculate the true Coulomb potentials in DFT? That is to say, we do not use Ewald, but only use th 1/r type. I know it can be realized in classical calculations, but i did not find the path to get it in QE.

	

	Thanks a lot.

	

	Jiayu






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	-------------------------------------------

	Jiayu Dai

	Department of PhysicsNational University of Defense Technology, 

	Changsha, 410073, P R China

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