95 lines
4.8 KiB
ReStructuredText
95 lines
4.8 KiB
ReStructuredText
============================================
|
||
Developping new functionals for KS or RS-DFT
|
||
============================================
|
||
|
||
The very basics
|
||
===============
|
||
|
||
To develop new functionals for |DFT| (or |RSDFT|) to be used in the SCF programs (:ref:`ks_scf` or :ref:`rs_ks_scf` ) or in multi-configurational |RSDFT| (see `<https://gitlab.com/eginer/qp_plugins_eginer>`_), you need to specify, at the end of the day, two things:
|
||
|
||
* *exchange/correlation* **energy functionals** used to compute the **energy**
|
||
|
||
* *exchange/correlation* **potentials** for (alpha/beta electrons) used to **optimize the wave function**
|
||
|
||
|
||
The providers to define such quantities, and then used by all the all the |DFT| programs, are (see :ref:`module_dft_one_e`):
|
||
|
||
* :c:data:`energy_x` and :c:data:`energy_c` : the *exchange* and *correlation* energy functionals (see :file:`e_xc_genera l.irp.f`)
|
||
|
||
* :c:data:`potential_x_alpha_ao` and :c:data:`potential_x_beta_ao` : the exchange potential for alpha/beta electrons on the |AO| basis (se e :file:`pot_general.irp.f`)
|
||
|
||
* :c:data:`potential_c_alpha_ao` and :c:data:`potential_c_beta_ao` : the correlation potential for alpha/beta electrons on the |AO| basis ( see :file:`pot_general.irp.f`)
|
||
|
||
From the |AO| basis, the providers for the exchange/correlation potentials of alpha/beta electrons on the |MO| basis are automatically obtained by a |AO| --> |MO| transformation.
|
||
|
||
So, at the end of the day, adding a new functional consists only in **setting a new value to these providers**.
|
||
|
||
|
||
The general philosphy
|
||
---------------------
|
||
|
||
The directory **functionals** contains only files ending with .irp.f whose name being the name of a specific functional.
|
||
All files in *a_functional*.irp.f **must** contain **at least** the following providers
|
||
|
||
* :c:data:`energy_x_a_functional` and :c:data:`energy_c_a_functional` which are of course the exchange and correlation energies
|
||
|
||
* :c:data:`potential_x_alpha_ao_a_functional` and :c:data:`potential_x_beta_ao_a_functional` which are the exchange alpha/beta potentials
|
||
|
||
* :c:data:`potential_c_alpha_ao_a_functional` and :c:data:`potential_c_beta_ao_a_functional` which are the correlation alpha/beta potentials
|
||
|
||
For instance, the file :file:`sr_lda.irp.f` contains the following providers
|
||
|
||
* :c:data:`energy_x_sr_lda` and :c:data:`energy_c_sr_lda` which are of course the exchange and correlation energies
|
||
|
||
* :c:data:`potential_x_alpha_ao_sr_lda` and :c:data:`potential_x_beta_ao_sr_lda` which are the exchange alpha/beta potentials
|
||
|
||
* :c:data:`potential_c_alpha_ao_sr_lda` and :c:data:`potential_c_beta_ao_sr_lda` which are the correlation alpha/beta potentials
|
||
|
||
|
||
Therefore, if you want to develop a new functional, just design a provider
|
||
|
||
To use a functional
|
||
|
||
Using the density for DFT calculations in the |QP|
|
||
==================================================
|
||
|
||
Different ways of defining the density for the DFT
|
||
--------------------------------------------------
|
||
|
||
There are many ways of defining a density, and the keyword to define it is :option:`density_for_dft density_for_dft`.
|
||
Here are the following options for that keyword:
|
||
|
||
* "KS" : density is obtained from **a single Slater determinant**
|
||
|
||
* "WFT" : density is obtained from **the wave function** which is stored in the |EZFIO| data base
|
||
|
||
* "input_density" : a one-body density matrix on the |MO| basis is read from the |EZFIO| data base, and the density is built from there (see :c:data:`data_one_e_dm_alpha_mo`)
|
||
|
||
* "damping_rs_dft" : damped density between "WFT" and "input_density" with the damping factor :option:`density_for_dft damping_for_rs_dft`.
|
||
|
||
.. note::
|
||
If an |MO| basis is already defined in the |EZFIO| data base, the one-body density matrices will be defined
|
||
according to this |MO| basis. For instance, if "KS", the density constructed will be density of a single Slater
|
||
determinant built with the current |MO| basis stored in the |EZFIO| data base.
|
||
|
||
Once that you have defined how to define the density, you can easily access to the providers associated to it.
|
||
|
||
|
||
Value of the density and its gradients in real space
|
||
----------------------------------------------------
|
||
|
||
The density and its gradients evaluated on all grid points are (see :ref:`module_dft_utils_in_r`):
|
||
|
||
* :c:data:`one_e_dm_alpha_at_r` and :c:data:`one_e_dm_beta_at_r` : alpha/beta density at grid points
|
||
|
||
* :c:data:`one_e_dm_and_grad_alpha_in_r`, :c:data:`one_e_dm_and_grad_beta_in_r`: alpha/beta gradients (and densities)
|
||
|
||
If you want to evaluate the density and its gradients at a given point in space, please refer to:
|
||
|
||
* :c:func:`density_and_grad_alpha_beta_and_all_aos_and_grad_aos_at_r`
|
||
|
||
If you use these *providers* and subroutines, the density computed will be coherent with the choice of density that you specified
|
||
with :option:`density_for_dft density_for_dft`, and it will impact automatically the general providers of :ref:`module_dft_one_e`.
|
||
|
||
|