Interface pinning calculations

Interface pinning uses the [math]\displaystyle{ Np_zT }[/math] ensemble where the barostat only acts along the [math]\displaystyle{ z }[/math] direction. This ensemble uses a Langevin thermostat and a Parrinello-Rahman barostat with lattice constraints in the remaining two dimensions. The solid-liquid interface must be in the [math]\displaystyle{ x }[/math]-[math]\displaystyle{ y }[/math] plane perpendicular to the action of the barostat.

Set the following tags for the interface pinning method:

OFIELD_Q6_NEAR

Defines the near-fading distance [math]\displaystyle{ n }[/math].

OFIELD_Q6_FAR

Defines the far-fading distance [math]\displaystyle{ f }[/math].

OFIELD_KAPPA

Defines the coupling strength [math]\displaystyle{ \kappa }[/math] of the bias potential.

OFIELD_A

Defines the desired value of the order parameter [math]\displaystyle{ A }[/math].

The following example INCAR file calculates the interface pinning in sodium:

TEBEG = 400                   # temperature in K
POTIM = 4                     # timestep in fs
IBRION = 0                    # run molecular dynamics
ISIF = 3                      # use Parrinello-Rahman barostat for the lattice
MDALGO = 3                    # use Langevin thermostat
LANGEVIN_GAMMA_L = 3.0        # friction coefficient for the lattice degree of freedoms (DoF)
LANGEVIN_GAMMA = 1.0          # friction coefficient for atomic DoFs for each species
PMASS = 100                   # mass for lattice DoFs
LATTICE_CONSTRAINTS = F F T   # fix x-y plane, release z lattice dynamics
OFIELD_Q6_NEAR = 3.22         # near fading distance for function w(r) in Angstrom
OFIELD_Q6_FAR = 4.384         # far fading distance for function w(r) in Angstrom
OFIELD_KAPPA = 500            # strength of bias potential in eV/(unit of Q)^2
OFIELD_A = 0.15               # desired value of the Q6 order parameter

---