Input File Description

Program: fdepw.x / PWscf / Quantum Espresso

TABLE OF CONTENTS

INTRODUCTION

&SYSTEM

fde_kin_funct | fde_xc_funct | fde_nspin | fde_print_density | fde_print_density_frag | fde_print_embedpot | fde_split_mix | fde_cell_split

&ELECTRONS

fde_frag_charge | fde_init_rho

INTRODUCTION

Purpose of fdepw.x: running a subsystem dft calculation. The fragments are almost
                    independent KS calculation communicating with each other through MPI.

One input file per fragment in the format, using the same prefix but different number.
For example: somename.scf_0.in
             somename.scf_1.in
             ...
             somename.scf_N.in

The format of the input file is the same as a pwscf input file.
A few keywords have been added to the SYSTEM and ELECTRONS namelists.
Their explanation is reported here.
   

Namelist: SYSTEM

fde_kin_funct CHARACTER
Default: 'LC94'
The kinetic energy density functional to be used to evaluate the non-additive
kinetic energy and potential.
Selected GGA functionals are implemented:
    'TF' : Thomas-Fermi LDA
    'VW' : Von Weizsacker (unstable)
    'DGE2'
    'LLP'
    'PW86'
    'LC94' : Default
    'APBEK'
    'revAPBEK' : Recommended
         
fde_xc_funct CHARACTER
Default: 'SAME'
The xc density functional to be used to evaluate the non-additive
kinetic energy and potential. By default the same functional is used within
and across the fragments.
         
fde_nspin INTEGER
Default: 1
Determines wheter the supersystem density will be spin polarized:
    1 : Spin unpolarized
    2 : Spin polarized

If the nspin variable of at least one of fragment is equal to 2, then
fde_nspin NEEDS to be eqaual to 2 for all the fragments.
This allows to have one or more fragments treated openshell while the others
are close shell.
         
fde_print_density LOGICAL
Default: .false.
Print the total density to a .pp file at the end of the calculation.
         
fde_print_density_frag LOGICAL
Default: .false.
Print the fragment density to a .pp file at the end of the calculation.
         
fde_print_embedpot LOGICAL
Default: .false.
Explicitly calculate the embedding potential of the fragment and
print it to a .pp file at the end of the calculation.
Make sure this keyword is .true. only for a single fragment, or eQE will
arbitrarely print it only for the fragment with the lowest index.
The embedding potential is represented into the smaller electronic cell.
         
fde_split_mix LOGICAL
Default: .true.
Dynamically adjust the mixing_beta parameter of the fragment along the scf cycle.
Helps speeding up convergence and stability.
         
fde_cell_split(i), i=1,3 REAL
Default: fde_cell_split(i)=1.D0
Flag to define the dimension of each fragment electronic cell.
By default the electronic cell and the supersystem cell are the same,
but a huge increase in efficiency can be achieved if the fragment is small
enough compared to the total system so that its electronic structure can
be confined within a cell which is a fraction of the supersystem cell using this variable.
Each direction can be scaled independently.
Although any value between 0. and 1. can be set, the code will round it to be one of the
following allowed fractions:
    1/5
    1/4
    1/3
    2/5
    1/2
    3/5
    2/3
    3/4
    4/5
    1/1
And it might be further changed so that the grid points match across all the subsystems.
         

Namelist: ELECTRONS

fde_frag_charge REAL
Default: 0.D0
Change the number of electrons assigned to a fragment. Default = 0.0 neutral fragment.
The sum of the charges across all fragments needs to be 0.0
         
fde_init_rho LOGICAL
Default: .false.
Electronic structure initial guess:
    .false. = Superposition of atomic densities
    .true.  = Density of the isolated fragmentsnn
         
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