This example shows how to calculate the minimum energy path (MEP) 
by using the nudged elastic band (NEB) method in conjunction with 
the Effective Screening Medium Method (ESM) and constant bias potential 
(constant-mu) method.

Before starting this example, see also examples for the ESM method in
pw.x (PW/examples/ESM_example).

The example calculation proceeds as follows:

1) make an NEB calculation for H atom diffusion on Al(001) surface with
   ordinaly periodic boundary condition (no ESM),
   (input=Al001+H_pbc.in, output=Al001+H_pbc.out). This calculation 
   shows the MEP of H atom (Bridge site -> top site -> bridge site).
   This is a reference calculation for the following ESM calculations.

2) make an NEB calculation for H atom diffusion on Al(001) surface with
   ESM (bc3), (input=Al001+H_bc3.in, output=Al001+H_bc3.out).

3) repeat #2 under a constant bias potential (constant-mu) condition.
   The target Fermi energy is set to that for the initial geometory
   of #2 system. This Fermi energy is the reference of the bias potential.

4) repeat #3 but with a lower target Fermi energy (-0.5V)

5) repeat #3 but with a higher target Fermi energy (+0.5V)
