@@ -151,19 +151,6 @@ The ``fix npt`` allows us to impose both a temperature of :math:`300\,\text{K}`
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(with a damping constant of :math: `1000 \,\text {fs}`). With the ``iso `` keyword,
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the three dimensions of the box will be re-scaled simultaneously.
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- .. figure :: figures/water-light.png
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- :alt: Water reservoir from molecular dynamics simulations
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- :class: only-light
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-
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- .. figure :: figures/water-dark.png
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- :alt: Water reservoir from molecular dynamics simulations
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- :class: only-dark
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-
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- .. container :: figurelegend
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-
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- Figure: The water reservoir after equilibration. Oxygen atoms are in red, and
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- hydrogen atoms are in white.
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-
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Let us output the system into images by adding the following commands to **water.lmp **:
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.. code-block :: lammps
@@ -212,9 +199,20 @@ adding the following lines into **water.lmp**:
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The final state is saved in a binary file named **water.restart **.
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Run the input using LAMMPS. The system reaches its equilibrium temperature
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after just a few picoseconds, and its equilibrium density after approximately
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- 10 picoseconds (Fig.~\r ef{fig:PEG-density}). A snapshot of the equilibrated
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- system can also be seen in Fig.~\r ef{fig:PEG-water}.
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+ 10 picoseconds.
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+ .. figure :: figures/water-light.png
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+ :alt: Water reservoir from molecular dynamics simulations
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+ :class: only-light
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+
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+ .. figure :: figures/water-dark.png
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+ :alt: Water reservoir from molecular dynamics simulations
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+ :class: only-dark
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+
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+ .. container :: figurelegend
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+
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+ Figure: The water reservoir after equilibration. Oxygen atoms are in red, and
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+ hydrogen atoms are in white.
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.. admonition :: Note
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:class: non-title-info
@@ -330,19 +328,6 @@ Let us create images of the systems:
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acolor OAlc darkred adiam OAlc 2.6
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thermo 500
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- .. figure :: figures/solvatedPEG_light.png
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- :alt: PEG in water as simulated with LAMMPS
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- :class: only-light
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-
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- .. figure :: figures/solvatedPEG_dark.png
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- :alt: PEG in water as simulated with LAMMPS
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- :class: only-dark
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-
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- .. container :: figurelegend
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-
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- Figure : The PEG molecule solvated in water. Water is represented as a
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- transparent field for clarity.
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-
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Finally, to perform a short equilibration and save the final state to
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a **.restart ** file, add the following lines to the input:
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@@ -358,7 +343,19 @@ sure that the temperature remains close to the
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target value of :math: `300 ~\text {K}` throughout the entire simulation, and that
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the volume and total energy are almost constant, indicating
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that the system was in a reasonable configuration from the start.
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- See a snapshot of the system in Fig.~\r ef{fig:PEG-solvated}.
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+
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+ .. figure :: figures/solvatedPEG_light.png
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+ :alt: PEG in water as simulated with LAMMPS
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+ :class: only-light
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+
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+ .. figure :: figures/solvatedPEG_dark.png
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+ :alt: PEG in water as simulated with LAMMPS
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+ :class: only-dark
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+
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+ .. container :: figurelegend
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+
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+ Figure : The PEG molecule solvated in water. Water is represented as a
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+ transparent field for clarity.
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Stretching the PEG molecule
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===========================
@@ -389,22 +386,10 @@ following lines to **pull.lmp**:
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These lines identify the oxygen atoms (type OAlc) at the ends of the PEG
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molecule and calculates their center of mass along the :math: `x`-axis. It then
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- divides these atoms into two groups, ``end1 `` (i.e.,~ the OAlc atom to
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- the right of the center) and ``end2 `` (i.e.,~ the OAlc atom to the right
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+ divides these atoms into two groups, ``end1 `` (i.e., the OAlc atom to
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+ the right of the center) and ``end2 `` (i.e., the OAlc atom to the right
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of the center), for applying force during the stretching process.
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- .. figure :: figures/pulled_peg_light.png
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- :alt: PEG in water as simulated with LAMMPS
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- :class: only-light
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-
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- .. figure :: figures/pulled_peg_dark.png
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- :alt: PEG in water as simulated with LAMMPS
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- :class: only-dark
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-
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- .. container :: figurelegend
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-
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- Figure: PEG molecule stretched along the :math: `x` direction in water.
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-
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Add the following ``dump `` command to create images of the system:
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.. code-block :: lammps
@@ -424,20 +409,6 @@ the following lines to **pull.lmp**:
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fix mynvt all nvt temp 300 300 100
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fix myrct PEG recenter 0 0 0 shift all
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- .. figure :: figures/PEG-distance-dm.png
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- :class: only-dark
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- :alt: Evolution of the polymer radius of gyration
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-
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- .. figure :: figures/PEG-distance.png
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- :class: only-light
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- :alt: Evolution of the polymer radius of gyration
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-
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- .. container :: figurelegend
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-
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- Figure: a) Evolution of the radius of gyration :math: `R_\text {gyr}` of the PEG molecule,
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- with the force applied starting at :math: `t = 15 \,\text {ps}`. b) Histograms of
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- the dihedral angles of type 1 in the absence (orange) and in the presence (blue) of the applied force.
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-
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To investigate the stretching of the PEG molecule, let us compute its radius of
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gyration :cite: `fixmanRadiusGyrationPolymer1962a ` and the angles of its dihedral
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constraints using the following commands:
@@ -481,15 +452,40 @@ Each applied force has a magnitude of :math:`10 \, \text{kcal/mol/Å}`, correspo
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This value was chosen to be sufficiently large to overcome both the thermal agitation and
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the entropic contributions from the molecules.
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+ .. figure :: figures/pulled_peg_light.png
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+ :alt: PEG in water as simulated with LAMMPS
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+ :class: only-light
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+
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+ .. figure :: figures/pulled_peg_dark.png
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+ :alt: PEG in water as simulated with LAMMPS
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+ :class: only-dark
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+
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+ .. container :: figurelegend
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+
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+ Figure: PEG molecule stretched along the :math: `x` direction in water.
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+
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Run the **pull.lmp ** file using LAMMPS. From the generated images of the system,
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- you should observe that the PEG molecule eventually aligns
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- in the direction of the applied force (as seen in Fig.~\r ef{fig:PEG-in-water}).
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- The evolutions of the radius of gyration over
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- time indicates that the PEG quickly adjusts to the external force
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- (Fig.~\r ef{fig:PEG-distance}\, a). Additionally, from the values of the dihedral angles
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+ you should observe that the PEG molecule eventually aligns in the direction of
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+ the applied force. The evolutions of the radius of gyration over
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+ time indicates that the PEG quickly adjusts to the external force. Additionally,
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+ from the values of the dihedral angles
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printed in the **pull.dat ** file, you can create a histogram
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of dihedral angles for a specific type. For example, the angle :math: `\phi ` for dihedrals
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- of type 1 (C-C-OE-C) is shown in Fig.~\r ef{fig:PEG-distance}\, b.
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+ of type 1 (C-C-OE-C) is shown below.
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+
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+ .. figure :: figures/PEG-distance-dm.png
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+ :class: only-dark
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+ :alt: Evolution of the polymer radius of gyration
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+
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+ .. figure :: figures/PEG-distance.png
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+ :class: only-light
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+ :alt: Evolution of the polymer radius of gyration
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+
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+ .. container :: figurelegend
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+
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+ Figure: a) Evolution of the radius of gyration :math: `R_\text {gyr}` of the PEG molecule,
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+ with the force applied starting at :math: `t = 15 \,\text {ps}`. b) Histograms of
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+ the dihedral angles of type 1 in the absence (orange) and in the presence (blue) of the applied force.
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Tip: using external visualization tools
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