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GULP input

Let's go through the file gulp1a.in as an example:

opti dist comp conp
 cell
 3.0000000 3.0000000 3.0000000 90 90 90
 fractional
 Au 0.0000000 0.0000000 0.0000000
 Au 0.0000000 0.5000000 0.5000000
 Au 0.5000000 0.0000000 0.5000000
 Au 0.5000000 0.5000000 0.0000000
 lennard 12 6
 Au core Au core 214180.2000 625.482 40.000 0 0

The first line gives some general GULP input flags (there are others).

  • opti: Automatically optimize structure geometry (in contrast to single).
  • dist, comp: Tells GULP to compare before-and-after neighbor distances and lattice constants.
  • conp: Constant-pressure simulation (i.e., the type of thermodynamic ensemble).

Other items:

  • cell: The next line gives the unit cell parameters a, b, c, alpha, beta, and gamma.
  • fractional: All atom coordinates are given in fractional terms rather than absolute Cartesian values.
  • Au ...: These lines give the identities and fractional positions of all the atoms in the cell.
  • lennard 12 6: Use the 12-6 form of the Lennard-Jones potential.
  • Au core Au core...: Gives LJ parameters that should be used for the Au-Au interaction, and also the potential cutoff.
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