exercises:2014_ethz_mmm:uv
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exercise:uv [2014/05/16 04:07] – dpasserone | exercise:2014_ethz_mmm:uv [2014/10/15 13:34] – oschuett | ||
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</ | </ | ||
- | Then source your profile file, as well as loading the modules: | + | Then source your profile file, as well as loading the modules, and copying this configuration file: |
< | < | ||
. ~/ | . ~/ | ||
module load intel/ | module load intel/ | ||
+ | cp ~danielep/ | ||
</ | </ | ||
Now you are able to run the **nwchem** code. | Now you are able to run the **nwchem** code. | ||
- | Copy all files from the directory: ** / | + | Download |
===== Calculation of the spectrum using linear response TDDFT ===== | ===== Calculation of the spectrum using linear response TDDFT ===== | ||
Line 103: | Line 104: | ||
</ | </ | ||
- | <note important> | + | <note important> |
+ | - List in a table the orbital energies for this system. Note that alpha and beta orbitals are listed, but they are degenerate in this case (alpha=beta). Search for the string " | ||
- Visualize homo and lumo with vmd. | - Visualize homo and lumo with vmd. | ||
- | - The excitation spectrum corresponds to transitions between occupied and unoccupied states. Look for this information in the file, and compare it with the peaks in the plot.</ | + | - The excitation spectrum corresponds to transitions between occupied and unoccupied states. Look for this information in the file, and compare it with the peaks in the plot. |
+ | </ | ||
+ | ===== Resonant ultraviolet excitation of water ===== | ||
+ | |||
+ | In this second part, we compute the time-dependent electron response to a quasi-monochromatic laser pulse tuned to a particular transition. | ||
+ | The spectrum obtained with linear response TDDFT can be also calculated by exciting the system through a laser pulse with a specific polarization along x, y, or z. | ||
+ | We will use the results of a calculation described [[http:// | ||
+ | |||
+ | {{ 730px-rt_tddft_h2o_resonant_spec_field.png? | ||
+ | |||
+ | |||
+ | Say we are interested in the excitation near 10 eV. We can clearly see this is a z-polarized transition (green on curve). To selectively excite this we could use a continuous wave E-field, which has a delta-function, | ||
+ | |||
+ | The relevant code section is: | ||
+ | < | ||
+ | rt_tddft | ||
+ | tmax 1000.0 | ||
+ | dt 0.2 | ||
+ | |||
+ | field " | ||
+ | type gaussian | ||
+ | polarization z | ||
+ | frequency 0.3768 | ||
+ | center 393.3 | ||
+ | width 64.8 | ||
+ | max 0.0001 | ||
+ | end | ||
+ | |||
+ | excite " | ||
+ | end | ||
+ | task dft rt_tddft | ||
+ | </ | ||
+ | |||
+ | Run now ** h2_resonant.nw ** on 4 cores: | ||
+ | |||
+ | < | ||
+ | bsub -n 4 -o resonant.out | ||
+ | </ | ||
+ | |||
+ | The run (follow with bpeek) will apply a field for a limited amount of time. This field will excite the system into a superposition of the ground state and the one excited state, which manifests as monochromatic oscillations. After the field has passed the dipole oscillations continue forever as there is no damping in the system. | ||
+ | There are 5000 MD steps. It will take about 10 minutes. At the end, cubefiles for the density at each timestep will be generated. | ||
+ | You can visualize the animation using vmd, using a script that cleans a bit (moving the cubes into another directory) | ||
+ | |||
+ | < | ||
+ | ./ | ||
+ | vmd -e animate.cube.vmd | ||
+ | </ | ||
+ | |||
+ | What you will see is the electron density difference between the initial state and an instant along the trajectory. | ||
+ | |||
+ | |||
+ | <note important> | ||
+ | - Plot from the output file the applied field: **grep -i Applied resonant.out | grep alpha > appl** | ||
+ | - Plot the z component of the induced dipole moment: **grep ipole resonant.out > dipole** | ||
+ | - Explain what you see in the vmd representation based on what you see on the previous plot | ||
+ | </ |
exercises/2014_ethz_mmm/uv.txt · Last modified: 2020/08/21 10:15 by 127.0.0.1