37 lines
2.2 KiB
Plaintext
37 lines
2.2 KiB
Plaintext
This directory has two input scripts that illustrates how to use fix
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charge_regulation in LAMMPS to perform coarse-grained molecular dynamics
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(MD) simulations with incorporation of charge regulation effects. The
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charge regulation is implemented via Monte Carlo (MC) sampling following
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the reaction ensemble MC approach, producing a MC/MD hybrid tool for
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modeling charge regulation in solvated systems.
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The script `in.chreg-acid` sets up a simple weak acid electrolyte
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(pH=7,pKa=6,pI=3). Four different types of MC moves are implemented:
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acid protonation & de-protonation, and monovalent ion pair insertion and
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deletion. Note here we have grouped all free monovalent ions into a
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single type, a physically natural choice on the level of coarse-grained
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primitive electrolyte models, which increases the calculation
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performance but has no effects on thermodynamic observables. The
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variables such as pH, pKa, pI, and lb at the top of the input script can
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be adjusted to play with various simulation parameters. The cumulative
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MC attempted moves and cumulative number of accepted moves, as well as,
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current number of neutral and charged acid particles, neutral and
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charged base particles (in this example always 0), and the current
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number of free cations and anions in the system are printed in the
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output.
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The script `in.chreg-polymer` sets up a weak poly-electrolyte chain of
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N=80 beads. Each bead is a weak acid with pKa=5 and solution has pH=7
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and monovalent salt chemical potential pI=3. In this example, we choose
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to treat salt ions, protons, and hydroxyl ions separately, which results
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in 5 types of MC moves: acid [type 1] protonation & de-protonation (with
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protons [type 4] insertion & deletion), acid [type 1] protonation &
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de-protonation (with salt cation [type 2] insertion & deletion), water
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self-ionization (insertion and deletion of proton [type4] and hydroxyl
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ion [type 5] pair), insertion and deletion of monovalent salt pair [type
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2 and type 3] , insertion and deletion of a proton [type4] and salt
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anion [type 3]. The current number of neutral and charged acid
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particles, the current number of free salt cations and anions, and the
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current number of protons and hydroxyl ions are printed in the output.
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