    ------------------------------------------------------------------------
    INPUT FILE DESCRIPTION

    Program: neb.x / NEB / Quantum Espresso (version: 6.6)
    ------------------------------------------------------------------------

    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
          INTERMEDIATE_IMAGE
          ...pw ATOMIC_POSITIONS card
          LAST_IMAGE
          ...pw ATOMIC_POSITIONS card
        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 ]

    ########################################################################
    | SUPERCARD: BEGIN/END
    | this supercard is enclosed within the keywords:
    |
    | BEGIN
    |    ... content of the supercard here ...
    | END
    |
    | The syntax of supercard's content follows below:

       ########################################################################
       | SUPERCARD: BEGIN_PATH_INPUT/END_PATH_INPUT
       | this supercard is enclosed within the keywords:
       |
       | BEGIN_PATH_INPUT
       |    ... content of the supercard here ...
       | END_PATH_INPUT
       |
       | The syntax of supercard's content follows below:

          ========================================================================
          NAMELIST: &PATH

             +--------------------------------------------------------------------
             Variable:       string_method

             Type:           CHARACTER
             Default:        'neb'
             Description:
                             A string describing the task to be performed. Options are:

                             'neb' :
                                  nudget-elastic-band

                             'smd' :
                                  string-method-dynamics
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       restart_mode

             Type:           CHARACTER
             Default:        'from_scratch'
             Description:
                             Options are:

                             'from_scratch' :
                                  from scratch

                             'restart' :
                                  from previous interrupted run
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       nstep_path

             Type:           INTEGER
             Description:    number of ionic + electronic steps
             Default:        1
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       num_of_images

             Type:           INTEGER
             Default:        0
             Description:    Number of points used to discretize the path
                             (it must be larger than 3).
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       opt_scheme

             Type:           CHARACTER
             Default:        'quick-min'
             Description:
                             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.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       CI_scheme

             Type:           CHARACTER
             Default:        'no-CI'
             Description:
                             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
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       first_last_opt

             Type:           LOGICAL
             Default:        .FALSE.
             Description:    Also the first and the last configurations are optimized
                             "on the fly" (these images do not feel the effect of the springs).
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       minimum_image

             Type:           LOGICAL
             Default:        .FALSE.
             Description:    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.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       temp_req

             Type:           REAL
             Default:        0.D0 Kelvin
             Description:    Temperature used for the langevin dynamics of the string.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       ds

             Type:           REAL
             Default:        1.D0
             Description:    Optimisation step length ( Hartree atomic units ).
                             If "opt_scheme"=="broyden", ds is used as a guess for the
                             diagonal part of the Jacobian matrix.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variables:      k_max, k_min

             Type:           REAL
             Default:        0.1D0 Hartree atomic units
             Description:    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.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       path_thr

             Type:           REAL
             Default:        0.05D0 eV / Angstrom
             Description:    The simulation stops when the error ( the norm of the force
                             orthogonal to the path in eV/A ) is less than path_thr.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       use_masses

             Type:           LOGICAL
             Default:        .FALSE.
             Description:    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"
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       use_freezing

             Type:           LOGICAL
             Default:        .FALSE.
             Description:    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.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       lfcpopt

             Type:           LOGICAL
             See:            fcp_mu
             Default:        .FALSE.
             Description:    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).
                             "fcp_mu" gives the target Fermi energy.
                             See the header of PW/src/fcp.f90 for documentation
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       fcp_mu

             Type:           REAL
             See:            lfcpopt
             Default:        0.d0
             Description:    If "lfcpopt" == .TRUE., gives the target Fermi energy [Ry].
                             One can specify the total charge of the system for the first
                             and last image by giving "fcp_tot_charge_first" and "fcp_tot_charge_last"
                             so that the Fermi energy of these systems will be the target value,
                             otherwise "first_last_opt" should be .TRUE.
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       fcp_tot_charge_first

             Type:           REAL
             See:            lfcpopt
             Default:        0.d0
             Description:    Total charge of the system ('tot_charge') for the first image.
                             Initial 'tot_charge' for intermediate images will be given by
                             linear interpolation of "fcp_tot_charge_first" and "fcp_tot_charge_last"
             +--------------------------------------------------------------------

             +--------------------------------------------------------------------
             Variable:       fcp_tot_charge_last

             Type:           REAL
             See:            lfcpopt
             Default:        0.d0
             Description:    Total charge of the system ('tot_charge') for the last image.
                             Initial 'tot_charge' for intermediate images will be given by
                             linear interpolation of "fcp_tot_charge_first" and "fcp_tot_charge_last"
             +--------------------------------------------------------------------

          ===END OF NAMELIST======================================================

          ========================================================================
          CARD: CLIMBING_IMAGES

             OPTIONAL CARD, NEEDED ONLY IF "CI_SCHEME" == 'MANUAL', IGNORED OTHERWISE !

             /////////////////////////////////////////
             // Syntax:                             //
             /////////////////////////////////////////

                CLIMBING_IMAGES
                   index1, index2, ... indexN

             /////////////////////////////////////////

             DESCRIPTION OF ITEMS:

                +--------------------------------------------------------------------
                Variables:      index1, index2, ... indexN

                Type:           INTEGER
                Description:    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.
                +--------------------------------------------------------------------

          ===END OF CARD==========================================================

       ### END OF SUPERCARD :  BEGIN_PATH_INPUT/END_PATH_INPUT ################

       ########################################################################
       | SUPERCARD: BEGIN_ENGINE_INPUT/END_ENGINE_INPUT
       | this supercard is enclosed within the keywords:
       |
       | BEGIN_ENGINE_INPUT
       |    ... content of the supercard here ...
       | END_ENGINE_INPUT
       |
       | The syntax of supercard's content follows below:

          Here comes the pw.x specific namelists and cards (see file: "" 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
               ...
             /
             ...

          ########################################################################
          | SUPERCARD: BEGIN_POSITIONS/END_POSITIONS
          | this supercard is enclosed within the keywords:
          |
          | BEGIN_POSITIONS
          |    ... content of the supercard here ...
          | END_POSITIONS
          |
          | The syntax of supercard's content follows below:

             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.

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

             ########################################################################
             | SUPERCARD: FIRST_IMAGE
             | this supercard starts with the keyword:
             |
             | FIRST_IMAGE
             |    ... content of the supercard here ...
             |
             | The syntax of supercard's content follows below:

                ========================================================================
                CARD: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

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

                ===END OF CARD==========================================================

             ### END OF SUPERCARD :  FIRST_IMAGE ####################################

             ########################################################################
             | SUPERCARD: INTERMEDIATE_IMAGE
             | this supercard starts with the keyword:
             |
             | INTERMEDIATE_IMAGE
             |    ... content of the supercard here ...
             |
             | REMARK:
             | There can be any number (including zero) of INTERMEDIATE_IMAGE supercards.
             |
             | The syntax of supercard's content follows below:

                ========================================================================
                CARD: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

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

                ===END OF CARD==========================================================

             ### END OF SUPERCARD :  INTERMEDIATE_IMAGE #############################

             ########################################################################
             | SUPERCARD: LAST_IMAGE
             | this supercard starts with the keyword:
             |
             | LAST_IMAGE
             |    ... content of the supercard here ...
             |
             | The syntax of supercard's content follows below:

                ========================================================================
                CARD: ATOMIC_POSITIONS { alat | bohr | angstrom | crystal | crystal_sg }

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

                ===END OF CARD==========================================================

             ### END OF SUPERCARD :  LAST_IMAGE #####################################

          ### END OF SUPERCARD :  BEGIN_POSITIONS/END_POSITIONS ##################

          Here can follow other pw specific cards ...

       ### END OF SUPERCARD :  BEGIN_ENGINE_INPUT/END_ENGINE_INPUT ############

    ### END OF SUPERCARD :  BEGIN/END ######################################

    This file has been created by helpdoc utility on Wed Dec 02 08:04:42 CET 2020