Ulf R. Pedersen Image for top bar on www.urp.dk

Interface Pinning (IP)

A versatile method for computing the solid-liquid Gibbs free-energy differences and constructing phase diagrams.

First papers on the IP method:

Direct calculation of the solid-liquid Gibbs free energy difference in a single equilibrium simulation
Ulf R. Pedersen
[J. Chem. Phys. 139, 104102 (2013)] [PDF] CC BY 3.0

Computing Gibbs free energy differences by interface pinning
Ulf R. Pedersen, Felix Hummel, Georg Kresse, Gerhard Kahl, Christoph Dellago
[Phys. Rev. B 88, 094101 (2013)] open access

Papers using and/or extending the method

Extensions of the interfacial pinning method and application to hard core systems
Vikram Thapar and Fernando A. Escobedo
[J. Chem. Phys. 141, 124117 (2014)]

Computing the crystal growth rate by the interface pinning method
Ulf R. Pedersen, Felix Hummel and Christoph Dellago
[J. Chem. Phys. 142, 044104 (2015)] open access

Implementation: LAMMPS

Add the collective density field to LAMMPS

1: Download and unpack the LAMMPS source code from lammps.sandia.gov.

2: Place fix_rhoKUmbrella.h and fix_rhoKUmbrella.cpp into the ./src/ folder.

3: Build and install LAMMPS as described on lammps.sandia.gov.

fix [name] [groupID] rhoKUmbrella [nx] [ny] [nz] [kappa] [anchor-point]

where U=0.5*kappa*(|rho_k|-anchor-point)^2 and k_i = (2 pi / L_i) * n_i .

Example: the Lennard-Jones model

Input file example: lmp.in
Two-phase configuration: halfhalf.restart.ascii
Input file to setup two-phase configuration: lmp_setup.in

Harmonic rho_k-field:
fix umbrella all rhoKUmbrella 16 0 0 4.0 26.00

Add rho_k to output:
thermo_style custom step temp pzz pe lz f_umbrella f_umbrella[1] f_umbrella[2] f_umbrella[3]

f_umbrella = energy of harmonic rho_k field
f_umbrella[1] = real part of rho_k
f_umbrella[2] = imagynary part of rho_k
f_umbrella[3] = |rho_k|

Other implementations