3.6 KiB
| authors |
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| xuhe |
Lattice Wannier function (LWF) model in MULTIBINIT
!!! tip
This feature is still under heavy development. Tests and feedbacks are welcome!
It is not recommended to be used in production at this stage.
Please contact the developers (x.he@uliege.be) for feedbacks and help.
LWF dynamics in MULTIBINIT
This lesson aims at showing how to build a LWF model and run a LWF dynamics calculation.
**Before beginning, we recommend the reading of the theory on Lattice Wannier functions in the literature cite:Rabe1995. The construction of LWF from the phonon band structure is covered in another tutorial. **
With this lesson, you will learn to:
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Building of the LWF model.
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Run the dynamics of LWF.
[TUTORIAL_README]
Before trying to run the LWF dynamics, you might consider to work in a subdirectory for this tutorial. Why not Work_lwfdyn?
How to build LWF models.
The LWF model consists of second order (harmonic) and higher order (anharmonic) interaction between the LWF's. The first step of building the LWF model is to construct the LWF and the harmonic Hamiltonian from the phonon band structure, which is covered in this tutorial. The tools for getting the anharmonic interaction are not ready for usage in the version 9.8. They will be released in the future.
How to use MULTIBINIT to run LWF dynamics
With the LWF model built and saved into a netcf file, we can run LWF dynamics calculation with MULTIBINIT. The input files for an example can be found at ~abinit/tests/tutomultibinit/Input/ . The input file can also be downloaded from: {% dialog tests/tutomultibinit/Input/tmulti6_1.abi %}
The netcdf file tmulti6_1.nc contains the LWF model, and tmulti6_1.abi is the input file. The input file is shown below. Note that the first line "lwf_pot_fname"
ncellmat = 8 0 0 0 8 0 0 0 8 # size of supercell, 3x3 matrix.
lwf_dynamics=3 # type of dynamics. 3: Berendsen thermostat
lwf_dt =1e-16 s # time step.
lwf_ntime = 3000 # number of time steps
lwf_nctime = 100 # write to netcdf history file per 100 steps.
lwf_taut = 1e-14 s # characteristic time for berendsen dynamics.
lwf_init_state=1 # initial state. 1: random amplitude.
lwf_var_temperature=1 # whether to do variable temperature calculation.
lwf_temperature_start=600.1 # Starting temperature.
lwf_temperature_end=0.1 # Ending temperature.
lwf_temperature_nstep=7 # number of temperature steps.
For a more realistic simulation, the size of the supercell, and the number of temperature steps should be increased.
To run the LWF dynamics, use the command below:
multibinit tmulti6_1.abi --F03 > tmulti6_1.log
For each temperature point, the temperature, kinetic energy, potential energy, and total energy will be output for every lwf_nctime step.
Iteration temperature(K) Ekin(Ha/uc) Epot(Ha/uc) ETOT(Ha/uc)
100 601.99469 1.90641E-03 3.70420E-04 2.27683E-03
200 419.24864 1.32768E-03 2.73706E-03 4.06475E-03
300 421.02202 1.33330E-03 5.28296E-03 6.61626E-03
......
A file ending with "_lwfhist.nc", which contains the trajectory of the LWF amplitudes, will be generated. By analyzing it, we can extract the information like heat capacity and susceptibility. If there is a structural phase transition, the critical temperature can also be found. The tools for doing these analyses are still under development.