NMM to setup an MD engine for the AD system.
To make the OPS engine, we also need to fill an engine_options dictionary with some OPS-specific and OpenMM-specific entries. All OPS engines must define n_steps_per_frame, the number of time actions per saved trajectory frame, and n_frames_max, an absolute maximum trajectory length. For the alanine dipeptide examples, we save every 20 fs (10 measures) and abort the trajectory if it reaches 40 ps:ArticleIn this example, we define two states, C7eq and R, similarly to ref 95. Given that we are employing a diverse force field, we use slightly different values for the angles. Our state C7eq is defined (in degrees) by 180 0 and 100 200 (wrapped periodically), whereas R is provided by 180 0 and -100 0. To convert between degrees and radians, we define deg = np.pi180. The code to define C7eq is:Just after making the OpenMM method, the OpenMM integrator, the OpenMM properties dictionary, as well as the OPS engine solutions dictionary, all of those can be combined to create on OpenMM-based OPS engine:and state R may be coded accordingly. For nonperiodic CVs, the equivalent kind is CVDefinedVolume, and it does not contain the period_min and period_max arguments. The periodic version makes it possible for the C7eq state to wrap across the periodic boundary in the variable: We define the state from 100 degrees to 200 degrees, despite the fact that the function reports values among -180 deg and 180 deg. We would get the precise very same behavior by setting lambda_max to -160 degrees. For any TPS simulation, we only should define the states you'll find no interfaces to define. 6.1.3. Setting up the Transition Network and Move Scheme. The transition network creates and contains all the ensembles to become sampled. Within this case, there is certainly only a single ensemble. Later examples will deal with sets of ensembles. The fixed and flexible path T ASICs are in the literature; references are indicated in superscripts length examples diverge here: the fixed path length TPS simulation makes use of a fixed path length network with path length 400 frames (eight ps), designed with:where the template can be a snapshot loaded from a PDB file with omm.snapshot_from_pdb(file.pdb). The template snapshot is going to be made use of again to supply the storage file using a template to automatically determine the sizes of numerous arrays to become saved. The above engine-creation command also associates a name with the engine, which makes it much easier to reload from storage for reuse. 6.1.two. Defining States and Interfaces. The collective variables of interest for alanine dipeptide would be the backbone and dihedrals. To make a collective variable for these angles, we use our wrapper around MDTraj's compute_dihedrals function:For the versatile path length, which can be greater in practice, we useThis one particular line of code selects involving the two approaches. Several state TPS is often set up similarly. For instance, a multiple state TPS with states A, B, and C (allowing all transitions) might be made Ncrease in friction66. Inside the CG pathway, IRSp53 emerges as a byNext, we set up the move scheme. For the TPS simulations, we only need a shooting move.NMM to set up an MD engine for the AD system. The OpenMM-based OPS engine is primarily a wrapper for the OpenMM Simulation object.