Theory · 1 methods
Protocols
What CAPS computes, as it computes it: the equation, its symbols with CAPS's defaults, when to use the method, the source file, the tests that check it, and any departure from the cited method.
21-step compression and decompression
Alternating NVT heating, NVT cooling and NPT compression up to a maximum pressure, then decompression stages, then a final NPT stage at the target conditions. It relaxes the density of glassy polymer cells far faster than plain NPT at room temperature.
Larsen et al. 2011, Table 1
| Symbol | Meaning | In CAPS |
|---|---|---|
| T_max | heating temperature | 600 K (choose Tg + 200–300 K) |
| P_max | largest pressure | 5 × 10⁴ bar (49 346 atm) |
| time scale | multiplies every duration | 1 (shortened runs are labelled) |
When to use it
Glassy polymer cells before property calculations. Rubbers far above Tg equilibrate with plain NPT. For long runs on a cluster, Export writes any CAPS protocol for LAMMPS (protocol Equilibration protocol): each stage its own fix and run in the same ensembles, temperatures and pressures (Nosé–Hoover), every length scaled by -var scale for a quick check, then NPT production with density.dat; the push-off stages limit each step to 0.1 Å instead of capping the Lennard-Jones force.
- Source
core/src/equilibrate.cpp- Tested by
- Protocol.Larsen21MatchesThePublishedSchedule · Equilibrate.RunsStagesContinuously; tests/test_relax.cpp LammpsData.ProtocolStages (the stages, their lengths in steps, the push-off substitute, production); the 21-step, annealing and push-off protocols written for the PS melt run through LAMMPS (shortened by -var scale)
- Departure from the reference
- none
References
- Larsen, G. S., Lin, P., Hart, K. E., Colina, C. M., "Molecular simulations of PIM-1-like polymers of intrinsic microporosity", Macromolecules 44, 6944–6951 (2011). doi:10.1021/ma200345v