[QE-users] ESM calculation with tot_charge in QE

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Dear Hong,

In the boundary condition bc1, i.e. the open boundary condition, we need to prepare a neutral system. Because there are divergent terms in the total energy and the electrostatic potential. If your system is neutral, i.e. tot_charge=0, you can get an appropriate result with ESM, but your system is charged, i.e. tot_charge!=0, you can not get a physically meaningful result.

In other boundary conditions such as bc2 and bc3, the ESM automatically introduce compensation charge. Thus the whole system is neutral. In other words, there are no divergent terms in the total energy and the electrostatic potential for bc2 and bc3.

As you can understand from above description, the problem is the divergent term. If you can ensure that the additional charge induced in the system with bc1 will completely be screened by another medium, you can use the bc1 boundary condition. In this case, the total energy and the electrostatic potential are physically meaningful values. In other words, the divergent term from another medium eliminates that from the system.

If you want to dig into the details of this, you can read the following paper: Phys Rev. B 96, 115429 (2017).

In short, you can not use bc1 with a charged system.

Best regard,
Minoru

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National Institute of Advanced Industrial Science and Technology,
Research Centre for Computational Design of Advanced Functional Materials
E-mail: minoru.otani at aist.go.jp
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________________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Honghui Wu <hhwuaa at connect.ust.hk>
Sent: Saturday, March 10, 2018 2:38:38 AM
To: users at lists.quantum-espresso.org
Subject: [QE-users] ESM calculation with tot_charge in QE

Dear all,

Can we use the charged system (tot_charge= a finite value) with the
vacuum-slab-vacuum boundary condition (esm_bc = 'bc1') in Quantum ESPRESSO?

In the OpenMX website, I find the ESM developer writes 'ESM.switch =
on1: Both ESM (I) and (II) are semi-infinite vacuum media. In this case,
note that the total charge of a calculation system should be neutral.
The keyword 'scf.system.charge' should be set to be zero.'.
However, I did not find the similar description of the esm_bc= 'bc1' :
Vacuum-slab-vacuum (open boundary conditions).  Does it mean we can use
the charged system (tot_charge= a finite value) with the
vacuum-slab-vacuum boundary condition in Quantum ESPRESSO?

Thank you!

Best regards,
Hong
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