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--- exercises:2018_uzh_acpc2:mol_sol [2018/05/03 12:35] – jglan
+++ exercises:2018_uzh_acpc2:mol_sol [2020/08/21 10:15] (current) – external edit 127.0.0.1
@@ Line 4: / Line 4: @@
 [[http://www1.lsbu.ac.uk/water/water_models.html|Water molecular models]] are computational techniques that have been developed in order to help discover the structure of water. In this section, you will be asked to calculate some physical properties based on classical molecular dynamics simulation. The TIP3/Fw model will be usded in the simulations.
-We have prepared a CP2K input file ''water.inp'' for running a MD simulation of liquid water using the force field from the first exercise (parametrized by [[https://aip.scitation.org/doi/pdf/10.1063/1.1884609|Praprotnik et al.]]). Download {{ :exercises:2017_uzh_acpc2:water.tar.gz |water.tar.gz}}
+We have prepared a CP2K input file ''water.inp'' for running a MD simulation of liquid water using the force field from the first exercise (parametrized by [[https://aip.scitation.org/doi/pdf/10.1063/1.1884609|Praprotnik et al.]]).
+<note important>Download {{ water.zip |water.zip}} and extract it.</note>
@@ Line 32: / Line 33: @@
   * Plot RMSD for the water at 300K and calculate corresponding diffusion coefficient, are they expected?
 </note>
+<note important>The diffusion coefficient is calculated using MSD but NOT RMSD.</note>
-In this exercise, we will compute the vibrational spectrum of water based on molecular dynamics. The spectra for water are available in this paper [[https://aip.scitation.org/doi/pdf/10.1063/1.1884609|https://doi.org/10.1063/1.1884609]].
+We will compute the vibrational spectrum, and dielectric constant of water based on molecular dynamics. The spectra for water are available in this paper [[https://aip.scitation.org/doi/pdf/10.1063/1.1884609|https://doi.org/10.1063/1.1884609]]. The provided program computes the correlation function of the (derivative of) the dipole moment and performs the Fourier transform.
+\begin{equation}
+A(\omega)\propto{\int\langle{\mu}({\tau}){\mu}(t+{\tau})\rangle_{\tau}e^{-i{\omega}t}d{t}},
+\label{eq:auto}
+\end{equation}
@@ Line 49: / Line 56: @@
 \end{equation}
+Compile the FORTRAN code, and execute the program
+<code>
+gfortran cpt_ir_diele.f90 -o cpt_ir_diele.o
+./cpt_ir_diele.o < dipole.in
+</code>
+<note>**TASK 4**
+  * Compute the IR spectrum and plot it, match the frequencies with vibrational mode.
+  * Compute the dielectric constant of water at 300K.
+  * Does IR or dielectric constant match the experimenal value? If not, why?
+</note>
 ===== Ramachandran plot =====
@@ Line 68: / Line 85: @@
 Visualize the structure ''glyala.pdb'' with VMD and determine the atomic indices of the atoms defining the dihedral angles.
 </note>
+<note important>//Note:// While VMD starts counting atoms from 0, CP2K starts counting from 1, i.e. the VMD indices need to be increased by 1.</note>
 With this knowledge at hand,
@@ Line 74: / Line 94: @@
 <note>**TASK 2**
-  - The atomic indices defining the dihedral indices in the input file ''geo.in'' are missing. Replace ''I1'' to ''I4'' by the atomic indices determined previously. //Note:// While VMD starts counting atoms from 0, CP2K starts counting from 1, i.e. the VMD indices need to be increased by 1.
+  - The atomic indices defining the dihedral indices in the input file ''geo.in'' are missing. Replace ''I1'' to ''I4'' by the atomic indices determined previously.
   - Use ''perform-gopt.sh'' to perform the grid of geometry optimizations.
   - Use gnuplot to plot the potential energy surface (we have provided a script ''epot.gp''). Which are the two most favoured conformations? <code> $ gnuplot</code><code> gnuplot > load "epot.gp"</code>
 </note>
 ===== Glyala in water =====
 Now, we will move to a more realistic system - Glyala in water. We will preformed a MD of glyala in water and save the trajectory.
@@ Line 87: / Line 106: @@
 <note>**TASK 6**
-   - Perform the molecular dynamics simulation using NVT ensemble at 300K.
+   - Perform the molecular dynamics simulation using NVT ensemble at 300K. Change TIMECON (i.e.500, 2000 fs) in the &THERMOSTAT section.
-   - Re-run the calculation using NVT ensemble with different TIMECON (500, 2000 fs) in the &THERMOSTAT section, and plot the total energy, temperature against time. Explain what you observe.
    - Determine from which step the system is equilibrated, plot the calculated properties and explain why.
    - Compute the O-O radial distribution function for water with acceptable statistics using 20 ps (after equilibration) of simulated time.
+   - Determine the solvation shell by calculating RDF of g$_{CO}$ (carbon atoms from glyala and oxygen atoms from water)
 </note>