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exercises:2014_uzh_molsim:nacl_free_energy

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exercises:2014_uzh_molsim:nacl_free_energy [2014/06/30 11:25] talirz |
exercises:2014_uzh_molsim:nacl_free_energy [2014/10/15 13:44] (current) oschuett |
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- Look into ''NaCl_pot.in'' and write down the formula used for the potential energy of the interaction between $\text{Na}^+$ and $\text{Cl}^-$ in Hartree atomic units. (2P) | - Look into ''NaCl_pot.in'' and write down the formula used for the potential energy of the interaction between $\text{Na}^+$ and $\text{Cl}^-$ in Hartree atomic units. (2P) | ||

- Use ''./potential_energy.sh'' to calculate the potential energy as a function of Na-Cl distance. Create a plot of the resulting potential energy profile in ''pot_profile'' and the mathematical formula. | - Use ''./potential_energy.sh'' to calculate the potential energy as a function of Na-Cl distance. Create a plot of the resulting potential energy profile in ''pot_profile'' and the mathematical formula. | ||

- | - What do you observe, when the distance approaches 1/2 of the simulation box? How might the finite size of the simulation box have impacted the MD simulation in the [[http://cp2k.org/exercise:mm_uzh:nacl_md|previous exercise]]? (2P) | + | - What do you observe, when the distance approaches 1/2 of the simulation box? How might the finite size of the simulation box have impacted the MD simulation in the [[nacl_md|previous exercise]]? (2P) |

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<note>**TASK 3** | <note>**TASK 3** | ||

- Perform the free energy integration and plot the free energy profile. | - Perform the free energy integration and plot the free energy profile. | ||

- | - In the [[http://cp2k.org/exercise:mm_uzh:nacl_md|previous exercise]], you determined the average time required for dissociation of Na-Cl. Is the free energy barrier consistent with the time scale determined before? //Hint:// Use the Arrhenius equation. You can obtain an estimate for the attempt frequency from the high-frequency oscillations in the Na-Cl distance in the previous exercise. (2P) | + | - In the [[nacl_md|previous exercise]], you determined the average time required for dissociation of Na-Cl. Is the free energy barrier consistent with the time scale determined before? //Hint:// Use the Arrhenius equation. You can obtain an estimate for the attempt frequency from the high-frequency oscillations in the Na-Cl distance in the previous exercise. (2P) |

</note> | </note> | ||

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<note>**TASK 4** | <note>**TASK 4** | ||

- | - In the [[http://cp2k.org/exercise:mm_uzh:h2o_md|previous exercise]], we computed the O-O radial distribution function for water with acceptable statistics using just 20 ps of simulated time. Give two reasons, why collecting enough statistics for the Na-Cl radial distribution function requires much longer simulation times (with our setup). | + | - In the [[h2o_md|previous exercise]], we computed the O-O radial distribution function for water with acceptable statistics using just 20 ps of simulated time. Give two reasons, why collecting enough statistics for the Na-Cl radial distribution function requires much longer simulation times (with our setup). |

- Compute the radial distribution function for the provided trajectory and plot it as a function of Na-Cl distance. | - Compute the radial distribution function for the provided trajectory and plot it as a function of Na-Cl distance. | ||

- Use the equations above to compute the free energy profile. Does it agree with the one constructed from the Shake Lagrange multipliers? | - Use the equations above to compute the free energy profile. Does it agree with the one constructed from the Shake Lagrange multipliers? | ||

</note> | </note> |

exercises/2014_uzh_molsim/nacl_free_energy.txt ยท Last modified: 2014/10/15 13:44 by oschuett

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