####################################################################### # 17 Jul 96 # # # # Example: Constraining particle with the CONSTRAIN CAVITY command # # # ####################################################################### # # # The CONSTRAIN CAVITY command creates a cavity constraint which # # imposes a spring-like force on atoms that try to exit through the # # wall. # # # # In this example, we create a single Ni FCC 3.5x3.5x3.5 cube. # # This cube is started with its atoms at 16000K and its is placed # # in an ellipsoidal cavity. Molecular dynamics is performed for # # 2000 steps, during which time atoms 'boil' off the cube into # # space and are reflected back by the ellipsoid walls. # # # # A COR file cavity.cor is written so that a movie can be made. # # Also an ESAVE file cavity.e is written to every 10 steps to check # # that energy is conserved. # # # ####################################################################### # The format of the CONSTRAIN CAVITY command is # # # # CONSTRAIN ELLIPSOID spring xc yc zc xa ya za # # or # # CONSTRAIN SPHERE spring xc yc zc radius # # # # where spring is the spring constant (dynes/cm) # # xc yc zc is the center of the cavity (angstroms) # # xa ya za are the ellipsoidal half-axises (angstroms) # # (analogous to spherical radii) # # radius is the sphere radius (angstroms) # # # ####################################################################### # # Read Nickel-Aluminum potential # read ../nial.txt # # Set large box (most of box will be empty) # box 12 12 12 # # Create a 3.5x3.5x3.5 FCC cube with one corner at the origin # particle 4 1 0.25 0.25 0.25 1 0.25 0.75 0.75 1 0.75 0.25 0.75 1 0.75 0.75 0.25 dup 4 1 0 0 dup 4 0 1 0 dup 4 0 0 1 # # Trim off remaining 0.5 cells # # NOTE: This leaves 'extra' layer on trailing surfaces, # so that every surface atom is one of the fcc unit cell # 'corners'. The result is the cube looks more symetrical. # select not box 0 0 0 3.5 3.5 3.5 remove # # Move cube toward center of box # select all move 4.25 4.25 4.25 # # Add ellipsoid cavity # constrain cavity sphere 1e5 6.0 6.0 6.0 4.0 2.0 2.0 # # Scale up to Ni unit cell length # scale 3.52 # # Set masses # select all # MASS1 is set in nialh.txt file mass MASS1 # # Set adiabatic simulation (total energy conserved) # clamp -1 # # Initialize high temperature # itemp 16000 # # Save energy every 10 time steps (to check conservation of energy) # esave 10 cavity.e # # Write initial coordinates (for make movie after) # write cor cavity.cor # # Perform 2000 simulations steps # Save coordinates after every 20 steps # repeat 100 cmd 20 write cor +cavity.cor end