------------------------------------------------------------------------ INPUT FILE DESCRIPTION Program: neb.x / NEB / Quantum Espresso ------------------------------------------------------------------------ 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 General input file structure: =============================================================================== 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 input ./neb.x -input\_images. For case 1) a file containing KEYWORDS has to be written (see below). These KEYWORDS tells the parser which part of the file regards neb specifics and which part regards the energy/force engine (at the moment only PW). After the parsing different files are generated: neb.dat, with neb specific variables and a set of pw_*.in PWscf input files like 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 input data (file neb.dat) : =============================================================================== &PATH ... / [ CLIMBING_IMAGES list of images, separated by a comma ] ======================================================================== NAMELIST: &PATH +-------------------------------------------------------------------- Variable: string_method Type: CHARACTER Default: 'neb' Description: a string describing the task to be performed: 'neb', 'smd' +-------------------------------------------------------------------- +-------------------------------------------------------------------- Variable: restart_mode Type: CHARACTER Default: 'from_scratch' Description: '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: 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. +-------------------------------------------------------------------- ===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==========================================================