# Input File Description

## Program: neb.x / NEB / Quantum ESPRESSO (version: 7.2)

> ### TABLE OF CONTENTS

> > INTRODUCTION

> > BEGIN

> > > BEGIN_PATH_INPUT

> > > > &PATH

> > > > > string_method | restart_mode | nstep_path | num_of_images | opt_scheme | CI_scheme | first_last_opt | minimum_image | temp_req | ds | k_max | k_min | path_thr | use_masses | use_freezing | lfcp | fcp_mu | fcp_thr | fcp_scheme

> > > > CLIMBING_IMAGES

> > > > > index1, index2, ... indexN

> > > BEGIN_ENGINE_INPUT

> > > > BEGIN_POSITIONS

> > > > > FIRST_IMAGE

> > > > > > ATOMIC_POSITIONS

> > > > > > TOTAL_CHARGE

> > > > > > > tot_charge

> > > > > INTERMEDIATE_IMAGE

> > > > > > ATOMIC_POSITIONS

> > > > > > TOTAL_CHARGE

> > > > > > > tot_charge

> > > > > LAST_IMAGE

> > > > > > ATOMIC_POSITIONS

> > > > > > TOTAL_CHARGE

> > > > > > > tot_charge

> ### INTRODUCTION

> >     Input data format: { } = optional, [ ] = it depends, | = or

> >     All quantities whose dimensions are not explicitly specified are in
> >     RYDBERG ATOMIC UNITS

> >     BEWARE: TABS, DOS <CR><LF> CHARACTERS ARE POTENTIAL SOURCES OF TROUBLE

> >     neb.x DOES NOT READ FROM STANDARD INPUT !

> >     There are two ways for running a calculation with neb.x:

> >     (1) specifying a file to parse with the ./neb.x -inp or ./neb.x -input
> >         command line option.

> >     (2) or specifying the number of copies of PWscf inputs with the ./neb.x -input_images

> >     For case (1) a file containing special KEYWORDS (aka SUPERCARDS) has to be
> >     written (see below). These KEYWORDS tell the parser which part of the file
> >     contains the neb specifics and which part contains the energy/force engine
> >     input (at the moment only PW).  After the parsing, different files are
> >     generated: neb.dat, with the neb specific variables, and a set of pw_*.in
> >     PWscf input files, i.e., one for each input position. All options for a
> >     single SCF calculation apply.

> >     The general structure of the file to be parsed is:
> >     ==================================================

> >     BEGIN
> >       BEGIN_PATH_INPUT
> >         ... neb specific namelists and cards
> >       END_PATH_INPUT

> >       BEGIN_ENGINE_INPUT
> >         ...pw specific namelists and cards
> >         BEGIN_POSITIONS
> >           FIRST_IMAGE
> >           ...pw ATOMIC_POSITIONS card
> >           ...pw TOTAL_CHARGE card (only for FCP)
> >           INTERMEDIATE_IMAGE
> >           ...pw ATOMIC_POSITIONS card
> >           ...pw TOTAL_CHARGE card (only for FCP)
> >           LAST_IMAGE
> >           ...pw ATOMIC_POSITIONS card
> >           ...pw TOTAL_CHARGE card (only for FCP)
> >         END_POSITIONS
> >         ... other pw specific cards
> >       END_ENGINE_INPUT
> >     END

> >     For case (2) neb.dat and all pw_1.in, pw_2.in ... should be already present.

> >     Structure of the NEB-only input data (file neb.dat):
> >     ====================================================

> >     &PATH
> >       ...
> >     /

> >     [ CLIMBING_IMAGES
> >        list of images, separated by a comma ]

## BEGIN

Syntax of this supercard is the following:

    BEGIN
      ... content of the supercard here ...
    END

and the content is:

## BEGIN_PATH_INPUT

Syntax of this supercard is the following:

    BEGIN_PATH_INPUT
      ... content of the supercard here ...
    END_PATH_INPUT

and the content is:

## Namelist: &PATH

string_method | CHARACTER
Default: | 'neb'

>     A string describing the task to be performed. Options are:

> `'neb' :`

>        nudget-elastic-band

> `'smd' :`

>        string-method-dynamics

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restart_mode | CHARACTER
Default: | 'from_scratch'

>      Options are:

> `'from_scratch' :`

>        from scratch

> `'restart' :`

>        from previous interrupted run

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nstep_path | INTEGER
Default: | 1

>     number of ionic + electronic steps

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num_of_images | INTEGER
Default: | 0

>     Number of points used to discretize the path
>     (it must be larger than 3).

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opt_scheme | CHARACTER
Default: | 'quick-min'

>     Specify the type of optimization scheme:

> `'sd' :`

>       steepest descent

> `'broyden' :`

>       quasi-Newton Broyden's second method (suggested)

> `'broyden2' :`

>       another variant of the quasi-Newton Broyden's
>       second method to be tested and compared with the
>       previous one.

> `'quick-min' :`

>       an optimisation algorithm based on the
>       projected velocity Verlet scheme

> `'langevin' :`

>       finite temperature langevin dynamics of the
>       string (smd only). It is used to compute the
>       average path and the free-energy profile.

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CI_scheme | CHARACTER
Default: | 'no-CI'

>     Specify the type of Climbing Image scheme:

> `'no-CI' :`

>       climbing image is not used

> `'auto' :`

>       original CI scheme. The image highest in energy
>       does not feel the effect of springs and is
>       allowed to climb along the path

> `'manual' :`

>       images that have to climb are manually selected.
>       See also CLIMBING_IMAGES card

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first_last_opt | LOGICAL
Default: | .FALSE.

>     Also the first and the last configurations are optimized
>     "on the fly" (these images do not feel the effect of the springs).

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minimum_image | LOGICAL
Default: | .FALSE.

>     Assume a "minimum image criterion" to build the path. If an atom
>     moves by more than half the length of a crystal axis between one
>     image and the next in the input (before interpolation),
>     an appropriate periodic replica of that atom is chosen.
>     Useful to avoid jumps in the initial reaction path.

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temp_req | REAL
Default: | 0.D0 Kelvin

>     Temperature used for the langevin dynamics of the string.

[Back to Top]

ds | REAL
Default: | 1.D0

>     Optimisation step length ( Hartree atomic units ).
>     If opt_scheme=="broyden", ds is used as a guess for the
>     diagonal part of the Jacobian matrix.

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k_max, k_min | REAL
Default: | 0.1D0 Hartree atomic units

>     Set them to use a Variable Elastic Constants scheme
>     elastic constants are in the range [ k_min, k_max ]
>     this is useful to rise the resolution around the saddle point.

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path_thr | REAL
Default: | 0.05D0 eV / Angstrom

>     The simulation stops when the error ( the norm of the force
>     orthogonal to the path in eV/A ) is less than path_thr.

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use_masses | LOGICAL
Default: | .FALSE.

>     If. TRUE. the optimisation of the path is performed using
>     mass-weighted coordinates. Useful together with quick-min
>     optimization scheme, if some bonds are much stiffer than
>     others. By assigning a larger (fictitious) mass to atoms
>     with stiff bonds, one may use a longer time step "ds"

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use_freezing | LOGICAL
Default: | .FALSE.

>     If. TRUE. the images are optimised according to their error:
>     only those images with an error larger than half of the largest
>     are optimised. The other images are kept frozen.

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lfcp | LOGICAL
Default: | .FALSE.
See: | fcp_mu

>     If .TRUE. perform a constant bias potential (constant-mu) calculation with
>     - ESM method (assume_isolated = 'esm' and esm_bc = 'bc2' or 'bc3' must be
>                   set in SYSTEM namelist) or
>     - ESM-RISM method (assume_isolated = 'esm' and esm_bc = 'bc1' must be set
>                        set in SYSTEM namelist, and trism = .TRUE. must be set
>                        set in CONTROL namelist).

>     fcp_mu gives the target Fermi energy.
>     See the header of PW/src/fcp_module.f90 for documentation

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fcp_mu | REAL
Default: | 0.d0
See: | lfcp

>     If lfcp == .TRUE., gives the target Fermi energy [eV].
>     One can specify the total charge of the system for the first
>     and last image by giving TOTAL_CHARGE cards
>     so that the Fermi energy of these systems will be the target value,
>     otherwise first_last_opt should be .TRUE.
>     For the initial charge of intermediate images, the TOTAL_CHARGE
>     is linearly interpolated between the initial and the final ones
>     unless the TOTAL_CHARGE is given in the input file.

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fcp_thr | REAL
Default: | 0.01D0 V
See: | lfcp

>     The simulation stops when the error ( the maximum of the force
>     acting on the FCP in V ) is less than fcp_thr.

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fcp_scheme | CHARACTER
Default: | 'lm'
See: | lfcp

>     Specify the type of optimization scheme for FCP:

> `'lm' :`

>       Line-Minimization method.

> `'newton' :`

>       Newton-Raphson method with diagonal hessian matrix.
>       Also, coupling with DIIS.

> `'coupled' :`

>       Coupled method with ionic positions.
>       This is available only if opt_scheme == 'broyden',
>       or 'broyden2'.

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## Card: CLIMBING_IMAGES

Optional card, needed only if CI_scheme == 'manual', ignored otherwise !

### Syntax:

> CLIMBING_IMAGES
> index1, index2, ... indexN

### Description of items:

> index1, index2, ... indexN | INTEGER

> >     index1, index2, ..., indexN are indices of the images to which the
> >     Climbing-Image procedure apply. If more than one image is specified
> >     they must be separated by a comma.

> [Back to Top]

## END_PATH_INPUT

## BEGIN_ENGINE_INPUT

Syntax of this supercard is the following:

    BEGIN_ENGINE_INPUT
      ... content of the supercard here ...
    END_ENGINE_INPUT

and the content is:

    Here comes the pw.x specific namelists and cards (see file: INPUT_PW.html or INPUT_PW.txt)
    with the exception of ATOMIC_POSITIONS cards, which are specified separately within the
    BEGIN_POSITIONS/END_POSITIONS supercard as described below.

    So the input that follows here is of the following structure:

       &CONTROL
          ...
       /
       &SYSTEM
         ...
       /
       &ELECTRONS
         ...
       /
       ...

## BEGIN_POSITIONS

Syntax of this supercard is the following:

    BEGIN_POSITIONS
      ... content of the supercard here ...
    END_POSITIONS

and the content is:

    NB:
    Atomic positions for all the images are specified within the BEGIN_POSITIONS / END_POSITIONS
    supercard, where each instance of ATOMIC_POSITIONS card is prefixed either by FIRST_IMAGE,
    INTERMEDIATE_IMAGE, or LAST_IMAGE keywords.
    IF lfcp == .TRUE., total charges for all images have to be specified with TOTAL_CHARGE cards.

    Note that intermediate images are optional, i.e., there can be none or any number of
    INTERMEDIATE_IMAGE images.

## FIRST_IMAGE

Syntax of this supercard is the following:

    FIRST_IMAGE
      ... content of the supercard here ...

and the content is:

## Card: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

    For the description of ATOMIC_POSITIONS card see file: INPUT_PW.html or INPUT_PW.txt

## Card: TOTAL_CHARGE

Optional card, needed only if lfcp == .TRUE.

### Syntax:

> TOTAL_CHARGE
> tot_charge

### Description of items:

> tot_charge | REAL

> >     tot_charge is the total charge of the system.

> [Back to Top]

## INTERMEDIATE_IMAGE

Syntax of this supercard is the following:

    INTERMEDIATE_IMAGE
      ... content of the supercard here ...

and the content is:

( Remark: There can be any number (including zero) of INTERMEDIATE_IMAGE supercards. )

## Card: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

    For the description of ATOMIC_POSITIONS card see file: INPUT_PW.html or INPUT_PW.txt

## Card: TOTAL_CHARGE

Optional card, needed only if lfcp == .TRUE.

### Syntax:

> TOTAL_CHARGE
> tot_charge

### Description of items:

> tot_charge | REAL

> >     tot_charge is the total charge of the system.

> [Back to Top]

## LAST_IMAGE

Syntax of this supercard is the following:

    LAST_IMAGE
      ... content of the supercard here ...

and the content is:

## Card: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

    For the description of ATOMIC_POSITIONS card see file: INPUT_PW.html or INPUT_PW.txt

## Card: TOTAL_CHARGE

Optional card, needed only if lfcp == .TRUE.

### Syntax:

> TOTAL_CHARGE
> tot_charge

### Description of items:

> tot_charge | REAL

> >     tot_charge is the total charge of the system.

> [Back to Top]

## END_POSITIONS

    Here can follow other pw specific cards ...

## END_ENGINE_INPUT

## END

This file has been created by helpdoc utility on Sat Mar 18 13:32:05 CET 2023.