[QE-users] Questions about work function of metals in water(implicit water)

[Li, Bingxin]

Dear all,

Recently I am using Environ + QE to calculate the work function of Mg(0001) surface in different environment (vacuum/implicit water).  Firstly I was doing a geometry optimisation calculation of Mg(0001) slab without environment packages. In this case, the fermi energy of the slab is -0.2249 eV and the vacuum potential is around 3.4713 eV(obtained using the pp.x and avg.x). Therefore, the work function can be simply calculated using 3.4713 – (-0.2249) = 3.6962 eV (which is close to the reference value: 3.62 eV).

Then I use the environment packages and turn on the implicit model, the input file for the environment part is as follows:

&ENVIRON
   !
   verbose = 0
   environ_thr = 1.D0
   environ_type = 'input'
   env_static_permittivity = 78.3(water)/1(vacuum)
   env_surface_tension = 0.D0
   env_pressure = 0.D0
   env_electrostatic = .true.
   !
/
&BOUNDARY
   !
   solvent_mode = 'full'
   !
/
&ELECTROSTATIC
   !
   pbc_correction = 'parabolic'
   pbc_dim = 2
   pbc_axis = 3
   tol = 5.D-13
   !
/

The calculations for the slab in vacuum/water were done without any errors. However, in the vacuum case, the fermi energy (considering the parabolic correction) of the slab is -3.2031 + 0.4671 = -2.736 eV. The vacuum (enviroment) potential is 3.105 eV (using pp.x and avg.x). The work function is vacuum with the environment package is 3.105 -  (-2.736) = 5.841 eV, which is not correct. I guess this error answer is due to the wrong vacuum potential. That is to say, the environment potential in this case should not calculate in the normal way (pp.x + avg.x) or the environment potential should be corrected in some way. However, I have no idea about how to obtain the correct environment(vacuum/water) potential when the environment packages are used. I was wondering that could anyone who knows how to calculate the work function of the metal slab in the implicit environment correctly please help me on this issue?

I am looking forward to your reply.

Best Regards,
Bingxin

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