These examples show how to use ABACUS to do basic SCF calculations.

Note:
- Three input files are required in the calculation: 
  - INPUT(control parameters)
  - STRU(structures) 
  - KPT(k points)
  
- The pseudopotential files (or numerical orbital files) are also needed:
  - the path of pseudopotential files (or numerical orbital files) are defined 
    by 'pseudo_dir' (or 'orbital_dir') in INPUT file
  - the file names are defined in ATOMIC_SPECIES (or NUMBERICAL_ORBITAL) block
    in STRU file

- set 'calculation' to 'scf' in INPUT file

- set 'basis_type' to 'pw' (Plane Wave basis) or 'lcao' (Linear Combination of 
  Atomic Orbitals basis) in INPUT file. 

- There are two algorithms implemented within LCAO method:
  - set "gamma_only" to "1", and only the Gamma point of k-points is used. 
    This is efficient for cluster or large system.
  - set "gamma_only" to "0", which is used when k-points are needed, for example, 
    calculate the band structures.  

- set 'ecutwfc' to define the enegy cutoff

- set 'scf_thr' to define the convergence precision of SCF iteration

- set 'scf_nmax' to define the maximum iteration numbers of the SCF