####################################################################### # # # Example: Calculate the surface energy of a 100 surface in Ni at 0K # # # ####################################################################### # # # # # METHOD # # # # Compare the energy of a lattice with no surface (repeating # # boundary conditions in three directions) with the energy of a # # lattice with one surface (repeating boundaries in two # # direction, a free surface in the other). The difference in # # energy will be due to the surface energy. Divide the energy # # difference by the surface area to get the surface energy. # # # # # ####################################################################### # # # Read in NiAl potential # read ../niai.txt # # Set the size of the simulation box # NX,NY,NZ are the number of unit cells in the X, Y and Z directions # calc NX=4 calc NY=4 calc NZ=4 # # # Create an FCC lattice with unit cell length of 1 angstrom # box NX NY NZ fill particle 4 1 1/4 1/4 1/4 1 1/4 3/4 3/4 1 3/4 1/4 3/4 1 3/4 3/4 1/4 fill go # # Scale lattice to unit cell length of Ni, 3.52 angstroms # Save scale factor in the variable SCALE for later use. # calc SCALE=3.52 scale SCALE # # # Write lattice energy per atom with repeating boundaries in three directions # surface off x y z write energy # # Write lattice energy per atom with free surface in x direction # surface on x write energy # # Calculate area of free surface (in angstroms) # # NX and NZ are the number of unit cells in the Y and Z directions # 2 is the number of surfaces (one each at X=0 and X=NX*SCALE) # SCALE is the size of the Ni unit cell in angtroms. # calc AREA=2*NY*NZ*SCALE^2 write AREA # # From XMD output, take the difference in lattice energy and divide # the area of the free surface. # # Note that the energy reported by the WRITE ENERGY command is the # lattice energy *per atom*. Multiply by the number of atoms (in # this case, 256) to obtain the total lattice energy. Then take # this lattice energy difference and divide by the surface # energy surface area to obtain the surface energy. # # # JR - 2 Nov 1998 # (Thanks to Hengzhong Zhang )