This command defines what model or application SPPARKS will run. There are 3 kinds of applications: on-lattice, off-lattice, and general.

On-lattice applications define a set of static sites in space on which events occur. The sites can represent a crystalline lattice, or be more disordered. The key point is that they are immobile and that each site's neighborhood of nearby sites can be specified. Here is the list of on-lattice applications SPPARKS currently includes:

Off-lattice applications define a set of mobile sites in space on which events occur. The sites typically represent particles. Each site's neighborhood of nearby sites is defined by a cutoff distance. Here is the list of off-lattice applications SPPARKS currently includes.

General applications require no spatial information. Events are defined by the application, as well as the influence of each event on others. Here is the list of general applications SPPARKS currently includes.

The general applications in SPPARKS can only be evolved via a kinetic Monte Carlo (KMC) solver, specified by the solve_style command. On-lattice and off-lattice applications can be evolved by either a KMC solver or a rejection kinetic Monte Carlo (rKMC) method or a Metropolis (MMC) method. The rKMC and MMC methods are specified by the sweep command. Not all on- and off-lattice applications support each option.

KMC models are sometimes called rejection-free KMC or the N-fold way or the Gillespie algorithm in the MC literature. The application defines a list of "events" and associated rates for each event. The solver chooses the next event, and the application updates the system accordingly. This includes updating of the time, which is done accurately since rates are defined for each event. For general applications the definition of an "event" is arbitrary. For on-lattice application zero or more possible events are typically defined for each site.

rKMC models are sometimes called null-event KMC or null-event MC. Sites are chosen via some method (see the sweep command), and an event on that site is then selected which is accepted or rejected. Again, the application defines the "events" for each site and associated rates which influence the acceptance or rejection. It also defines the null event which is essentially part of the rejection probability.

For KMC and rKMC models, a time is associated with each event (including the null event) by rates that the user defines. Thus event selection induces a time-accurate simulation. The MMC method is similar to the rKMC method, except that it is not time-accurate. It selects an event to perform and accepts or rejects it, typically based on an energy change in the system. There is no rate associated with the event, and no requirement that events be chosen with relative probabilities corresponding to their rates. The Metropolis method tends to evolve the system towards a low energy state. As with the rKMC method, the sweep command is used to determine how sites are selected.

For all three methods (KMC, rKMC, MMC) the rules for how events are defined and are accepted or rejected are discussed in the doc pages for the individual applications.

This table lists the different kinds of solvers and sweeping options that can be used for on- and off-lattice applications in SPPARKS. Serial and parallel refer to running on one or many processors. Sector vs no-sector is what is set by the sector command. The rKMC options are set by the sweep command. The MMC options are the same as for rKMC.

method	serial/no-sectors	serial/sectors	parallel/no-sectors	parallel/sectors
exact KMC	yes	yes	no	yes
rKMC random	yes	yes	no	yes
rKMC raster	yes	yes	no	yes
rKMC color	yes	yes	yes	yes
rKMC color/strict	yes	no	yes	no

Note that masking can also be turned on for rKMC algorithms via the sweep command if the application supports it. Off-lattice applications do not support the color or masking options.

app_style command