Hierarchical Strategy for Simple One-Component Polymer Melts¶
The module is an implementation of the existing hierarchical strategy [1] for the equilibration of simple one-component polymer melts in ESPResSO++.
Purpose of Module¶
To study the properties of polymer melts by numerical simulations, equilibrated configurations must be prepared. However, the relaxation time for high molecular weight polymer melts is huge and increases, according to reptation theory, with the third power of the molecular weight. Hence, an effective method for decreasing the equilibration time is required. The hierarchical strategy pioneered in Ref. [1] is a particularly suitable way to do this. The present module provides an integration of that method into the package ESPResSO++.
To decrease the relaxation time, microscopic monomers are coarse-grained by mapping each subchain with monomers onto a soft blob. A polymer chain, originally consisting of monomers, is replaced by a coarse-grained (CG) chain consisting of soft blobs linked by a harmonic bond potential, , and an angular bond-bending potential . Here is the distance and is the angle between consecutive bonds. The interactions between non-bonded soft blobs are taken into account by a repulsive pair potential . Here is the center-to-center distance between the two blobs, is a Gaussian function with variance and is the gyration radius of blob number . The gyration radius is in turn fluctuating. This fluctuation is controlled by the potential .
After equilibrating a configuration at very coarse resolution, each CG polymer chain is replaced with a more fine-grained (FG) chain. In this procedure, a CG blob is divided into several FG blobs. The center of mass (COM) of the FG blobs coincides with the position of the CG blob’s center, and is being kept fixed during the relaxation of the local conformation of the FG monomers within the CG blob.
To develop this module, the following classes have been implemented or modified (and may have been described in more detail elsewhere):
- A
VSpherePair
class for calculating - A
LangevinThermostatOnRadius
class for simulating the fluctuations of the radii of the blobs - A
VSphereSelf
class for calculating - A
FixedLocalTupleList
class for storing the N-tuple of particles consisting of both real and virtual particles - A
ConstrainCOM
class for conserving the COM of N FG blobs with the CG blob
Background Information¶
The implementation of this module is based on ESPResSO++. You can learn about ESPResSO++ from the following links:
- ESPResSO++ documentation: http://espressopp.github.io/ESPResSo++.pdf
- ESPResSO++ source code: https://github.com/espressopp/espressopp
Testing¶
Explanation of installation of ESPResSO++ can be found at:
After installing this module, an example can be run from hierarchical_strategy_for_one-component subdirectory of the examples folder using the run_example script to be found there.
Source Code¶
This module was merged into ESPResSo++ in the Pull Request: