Monte-Carlo

Running Monte-Carlo

To perform a (Grand-Canonical) Monte-Carlo simulation we must run TurboGAP in mc mode:

turbogap mc

The following files are written to every write_xyz = N steps

• mc.log: self-explanatory,
  • format: mc_step mc_move accepted E_trial E_current N_sites(trial) N_gcmc_species(trial)
• mc_all.xyz: an appended file which contains all accepted moves
• mc_trial.xyz: a single configuration which contains the trial move
• mc_current.xyz: a single configuration which contains the current accepted

Monte-Carlo Move Types

We can specify a number of Monte-Carlo trial move types, including doing molecular dynamics (hybrid Monte-Carlo) as trial moves. These include

• Displacement
• Swap (to swap atoms in the simulation box)
• Volume (for NPT)
• Insertion (for mu VT)
• Removal (for mu VT)
• MD (for hybrid Monte-Carlo)

Minimal Input File

! Species-specific info
atoms_file = 'atoms.xyz'
pot_file = 'gap_files/CO.gap'
n_species = 2
species = C O
masses = 12.01 15.99


mc_nsteps = 5000                         ! Number of mc trial steps to be performed

n_mc_types = 3                           ! Number of mc trial types
mc_types = 'move' 'insertion' 'removal'  ! MC types can be: 'insertion' 'removal' 'md' 'swap' 'move'
                                         !                  'volume'
mc_acceptance = 1 1 1                    ! Ratios for choosing the respective trial moves (all equally likely here)

mc_move_max = 0.2                        ! Maximum distance for the move of a particular particle

n_mc_mu = 1
mc_mu = 0.0                              ! gcmc: Chemical potential [eV], using a large one here
mc_species = 'O'                         ! gcmc: species to insert / remove
mc_min_dist = 0.1                        ! gcmc: minimum distance between particles for insertion


! Note: The following files are written to every write_xyz steps
!       mc.log: self-explanatory,
!          format: mc_step  mc_move  accepted  E_trial  E_current  N_sites(trial)
!                                                                     N_gcmc_species(trial)
!       mc_all.xyz:     an appended file which contains all accepted moves
!       mc_trial.xyz:   a single configuration which contains the trial move
!       mc_current.xyz: a single configuration which contains the current accepted

write_xyz = 200

Monte-Carlo options

Keyword	Definition	Optional	Type	Default	Used when	Example
mc_nsteps	Number of MC steps	N	Int	0	turbogap mc	mc_nsteps = 1000
n_mc_types	Number of MC types	N	Int	0	turbogap mc	n_mc_types = 2
mc_types	Types of MC trials	N	Str(s)	None	n_mc_types > 0	mc_types = 'volume' 'move'
mc_acceptance	Ratios of MC trial moves	N	Int(s)	None	n_mc_types > 0	mc_acceptance = 2 1
n_mc_swaps	Number of swap pairs (e.g. C O is one pair)	Y	Int	0	'swap' in mc_types	n_mc_swaps = 2
mc_swaps	Swap species pairs	Y	Strs	None	'swap' in mc_types	mc_swaps = 'C' 'O' 'N' 'C'
mc_move_max	Maximum displacement [A]	Y	Float	1.0	'move' in mc_types	mc_move_max = 0.5
mc_lnvol_max	Log volume max for volume moves.	Y	Float	0.01	'volume' in mc_types	mc_lnvol_max = 0.02
mc_min_dist	Minimum distance for insertion [A]	Y	Float	0.2	'insertion in mc_types	mc_min_dist = 0.1
mc_max_dist	Maximum distance for insertion [A]	Y	Float	10000000.0	'insertion in mc_types	mc_max_dist = 5.0
n_mc_mu	Number of chemical potentials/gcmc species	Y	Int	1	'insertion'/'removal' in mc_types	n_mc_mu = 2
mc_mu	Chemical potential(s) [eV]	Y	Float	0.0	'insertion'/'removal' in mc_types	mc_mu = -5.16 -2.25
mc_species	GCMC species	Y	Str	None	'insertion'/'removal' in mc_types	mc_species = 'O' 'H'
mc_relax	Relax MC trials prior to acc. evaluation	Y	Bool	.false.	turbogap mc	mc_relax = .true.
n_mc_relax_after	Number of specific trials to relax	Y	Int	0	mc_relax = .true.	n_mc_relax_after = 1
mc_relax_after	Relax specific MC trial types	Y	Str(s)	None	n_mc_relax_after > 0	mc_relax_after = 'volume'
mc_nrelax	Number of relaxation steps after trial	Y	Int	0	mc_relax = .true.	mc_nrelax = 50
mc_relax_opt	Optimisation for relaxing after steps	Y	Str	'gd'	mc_relax = .true.	mc_relax_opt = 'gd-box-ortho'
mc_hamiltonian	Use NVE for 'md' trials	Y	Bool	.false.	'md' in mc_types	mc_hamiltonian = .true.
mc_hybrid_opt	Optimisation for 'md' steps	Y	Str	'vv'	'md' in mc_types	mc_hybrid_opt = 'vv'
mc_write_xyz	Debug: read and write to files every step	Y	Bool	.false.	turbogap mc	mc_write_xyz = .true.