@@ -21,42 +21,30 @@ Stretching a polymer
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:class: only-light
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The goal of this tutorial is to use GROMACS and solvate a small
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- hydrophilic polymer in a reservoir of water.
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+ hydrophilic polymer in a reservoir of water.
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An all-atom description is used for both polymer and water. The polymer is
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- PolyEthylene Glycol (PEG). Once the system is properly
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- equilibrated at the desired temperature and pressure, a force is applied
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- to both ends of the polymer. The evolution of the polymer length
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- is measured, and the energetics of the system is measured.
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+ PolyEthylene Glycol (PEG). Once the system is properly equilibrated at the
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+ desired temperature and pressure, a force is applied to both ends of the
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+ polymer. The evolution of the polymer length is measured, and the energetics
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+ of the system is analyzed. This tutorial was inspired by a publication by
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+ |Liese2017 | and coworkers, in which molecular dynamics simulations are
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+ compared with force spectroscopy experiments :cite: `lieseHydrationEffectsTurn2017 `.
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..
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(GROMOS 54A7 force
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field :cite:`schmid2011definition`)
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(SPC flexible model :cite:`wu2006flexible`)
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-
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-
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- This tutorial was inspired by a |Liese2017 | by Liese and coworkers, in which
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- molecular dynamics simulations are
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- compared with force spectroscopy experiments :cite: `liese2017hydration `.
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-
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- .. |Liese2017 | raw :: html
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-
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- <a href="https://doi.org/10.1021/acsnano.6b07071" target="_blank">publication</a>
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-
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.. include :: ../../non-tutorials/recommand-salt.rst
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.. include :: ../../non-tutorials/needhelp.rst
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.. include :: ../../non-tutorials/GROMACS2024.2.rst
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Prepare the PEG molecule
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========================
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- Download the *peg.gro * file for the PEG molecule by clicking |download_H2O.data |.
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- The *peg.gro * file can be visualized using vmd, by typing in a terminal:
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-
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- .. |download_H2O.data | raw :: html
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-
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- <a href="https://raw.githubusercontent.com/gromacstutorials/gromacstutorials-inputs/main/level2/stretching-a-polymer/cubic-box/peg.gro" target="_blank">here</a>
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+ Download the |peg-gro | file for the PEG molecule by clicking. The
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+ **peg.gro ** file can be visualized using VMD, by typing in a terminal:
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.. code-block :: bash
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@@ -78,53 +66,35 @@ The *peg.gro* file can be visualized using vmd, by typing in a terminal:
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oxygen atoms (in red), and hydrogen atoms (in white). See
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the corresponding |video_peg_youtube |.
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- .. |video_peg_youtube | raw :: html
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-
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- <a href="https://www.youtube.com/watch?v=8ldIHP175TI&t=9s" target="_blank">video</a>
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+ Save **peg.gro ** in a new folder. Next to **peg.gro ** create an empty
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+ file named **topol.top **, and copy the following lines into it:
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- Save *peg.gro * in a new folder. Next to *peg.gro * create an empty
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- file named *topol.top *, and copy the following lines in it:
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-
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- .. code-block :: bw
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+ .. code-block :: bash
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[ defaults ]
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- ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ
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- 1 1 no 1.0 1.0
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+ ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ
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+ 1 1 no 1.0 1.0
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; Include forcefield parameters
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# include "ff/charmm35r.itp"
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# include "ff/peg.itp"
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- #include "ff/tip3p.itp
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+ # include "ff/tip3p.itp"
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[ system ]
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; Name
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- PEG
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+ PEG
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[ molecules ]
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; Compound # mols
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- PEG 1
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-
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- Next to *conf.gro * and *topol.top *, create a folder named *ff/ *, and copy
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- the following 3 *.itp * files into it: |download_charmm35r.itp |, |download_peg.itp |,
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- and |download_tip3p.itp |.
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-
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- .. |download_charmm35r.itp | raw :: html
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-
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- <a href="https://raw.githubusercontent.com/gromacstutorials/gromacstutorials-inputs/main/level2/stretching-a-polymer/cubic-box/ff/charmm35r.itp" target="_blank">charmm35r.itp</a>
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-
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- .. |download_peg.itp | raw :: html
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-
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- <a href="https://raw.githubusercontent.com/gromacstutorials/gromacstutorials-inputs/main/level2/stretching-a-polymer/cubic-box/ff/peg.itp" target="_blank">peg.itp</a>
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+ PEG 1
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- .. |download_tip3p.itp | raw :: html
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-
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- <a href="https://raw.githubusercontent.com/gromacstutorials/gromacstutorials-inputs/main/level2/stretching-a-polymer/cubic-box/ff/tip3p.itp" target="_blank">tip3p.itp</a>
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-
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- These 3 files contain the parameters for the PEG and the water molecules
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+ Next to **conf.gro ** and **topol.top **, create a folder named **ff/ **, and copy
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+ the following 3 **.itp ** files into it: |download_charmm35r.itp |, |download_peg.itp |,
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+ and |download_tip3p.itp |. These 3 files contain the parameters for the PEG and the water molecules
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with oxygen (OW) and hydrogen (HW) atoms.
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- Create an *inputs/ * folder next to *ff/ *, and create a new empty file
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- called *em.mdp *. Copy the following lines into it:
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+ Create an ** inputs/ ** folder next to ** ff/ * *, and create a new empty file
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+ called ** em.mdp * *. Copy the following lines into it:
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.. code-block :: bw
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@@ -142,11 +112,11 @@ called *em.mdp*. Copy the following lines into it:
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rvdw = 1
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pbc = xyz
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- Most of these commands have been seen in previous tutorials. The most
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- important command is * integrator = steep * , which set the algorithm
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- used by GROMACS as the steepest-descent,
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- which moves the atoms following the direction of the largest forces
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- until one of the stopping criteria is reached :cite: `debyeNaeherungsformelnFuerZylinderfunktionen1909 `.
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+ Most of these commands have been seen in previous tutorials. Arguably the
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+ most important command is `` integrator = steep `` , which sets the algorithm
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+ used by GROMACS as the steepest-descent method. This algorithm moves the
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+ atoms following the direction of the largest forces until one of the stopping
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+ criteria is reached :cite: `debyeNaeherungsformelnFuerZylinderfunktionen1909 `.
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Run the energy minimization using GROMACS by typing in a terminal:
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@@ -155,8 +125,8 @@ Run the energy minimization using GROMACS by typing in a terminal:
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gmx grompp -f inputs/em.mdp -c peg.gro -p topol.top -o em-peg
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gmx mdrun -deffnm em-peg -v -nt 8
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- The * -nt 8 * option limits the number of threads that GROMACS uses. Adjust
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- the number to your computer.
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+ The `` -nt 8 `` option limits the number of threads that GROMACS uses. Adjust
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+ the number to your computer.
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After the simulation is over, open the trajectory file with VMD by typing
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in a terminal:
@@ -166,19 +136,20 @@ in a terminal:
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vmd peg.gro em-peg.trr
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From VMD, the PEG molecule can be seen moving a little by the
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- steepest-descent algorithm.
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+ steepest-descent algorithm.
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- Before adding the water, let us reshape the box and recenter the PEG molecule
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- in the box. As a first step, let us use a cubic box of
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- lateral size :math: `2.6 ~\text {nm}`.
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+ Before adding the water, let us reshape the box and recenter the PEG
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+ molecule in the box. As a first step, let us use a cubic box of lateral
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+ size :math: `2.6 ~\text {nm}`.
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- .. code-block :: bash
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+ .. code-block :: bash
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- gmx trjconv -f em-peg.gro -s em-peg.tpr -o peg-recentered.gro -center -pbc mol -box 2.6 2.6 2.6
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+ gmx trjconv -f em-peg.gro -s em-peg.tpr -o peg-recentered.gro -center
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+ -pbc mol -box 2.6 2.6 2.6
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- Select * system * for both centering and output. The newly created *gro *
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- file named *peg-recentered.gro * will be used as a starting point
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- for the next step of the tutorial.
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+ Select `` system `` for both centering and output. The newly created ** . gro* *
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+ file named ** peg-recentered.gro ** will be used as a starting point for the
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+ next step of the tutorial.
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Solvate the PEG molecule
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========================
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