From 6ffdccb26d757558ebc01f7bb5ac735d90159197 Mon Sep 17 00:00:00 2001 From: eginer Date: Mon, 4 Feb 2019 19:43:39 +0100 Subject: [PATCH] added source/programmers_guide/new_ks.rst --- docs/source/programmers_guide/new_ks.rst | 136 ++++++++++++++++++++++- 1 file changed, 134 insertions(+), 2 deletions(-) diff --git a/docs/source/programmers_guide/new_ks.rst b/docs/source/programmers_guide/new_ks.rst index 58e87c2a..c60db8c8 100644 --- a/docs/source/programmers_guide/new_ks.rst +++ b/docs/source/programmers_guide/new_ks.rst @@ -2,6 +2,138 @@ Developping new functionals for KS or RS-DFT ============================================ -The |QP| contains all the basic quantities to run |DFT| or |RS-DFT| calculations: +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 ``_), 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 +--------------------- + +We have created a quite easy way to develop new functionals that is based on + +* the used of **your own external plugins** + +* the module :ref:`module_new_functionals` acting as **hub** + +A pictorial representation of the main dependencies can be seen here: + + .. image:: /_static/dependencies_func.pdf + :align: center + :width: 200px + :alt: Summary of dependencies + + +The main idea is the following: + + 1. Develop *new providers* for the new functionals (energy and potential for exchange and correlation) in some **external plugin**. + + * Example: + + * In an **external plugin** named **fancy_functionals**, you create *e_c_new_fancy_func* for the energy and *pot_ao_alpha_new_func* for the alpha potential + + * If you want to be able to use the |DFT| programs already available in the |QP|, these *providers* must use the providers for the density defined in :ref:`module_density_for_dft` and :ref:`module_dft_utils_in_r` (see below). + + + 2. Add the name of your **external plugin** to the :file:`NEED` in order to link your new providers to **new_functionals** + + * Example: + + * add **fancy_functionals** to the NEED file of **new_functionals** + + 3. Change the file :file:`e_xc_new_func.irp.f` and :file:`pot_xc_new_func.irp.f` to set the value of your new providers to the providers defined in **new_functionals** + + * Example: + + * for the exchange/correlation energy + + + .. code:: fortran + + BEGIN_PROVIDER[double precision, energy_x_new_functional, (N_states) ] + &BEGIN_PROVIDER[double precision, energy_c_new_functional, (N_states) ] + implicit none + BEGIN_DOC + ! energy_x_new_functional = define here your functional + ! energy_c_new_functional = define here your functional + END_DOC + energy_c_new_functional = e_c_new_fancy_func + energy_x_new_functional = e_x_new_fancy_func + + END_PROVIDER + + +4. Compile at the root of the |QP| + + * Example: + + + .. code:: bash + + cd ${QP_ROOT} + ninja + + +5. When you want to execute a program with your new functional, just set the options :option:`dft_keywords exchange_functional` and :option:`dft_keywords correlation_functional` to "my_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`. + -* Handling