TABLE OF CONTENTS
INTRODUCTION
&PATH
string_method | restart_mode | nstep_path | num_of_images | opt_scheme | CI_scheme | first_last_opt | temp_req | ds | k_max | k_min | path_thr | use_masses | use_freezing
CLIMBING_IMAGES index1, index2, ... indexN
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
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 |
|---|
| string_method |
CHARACTER |
| Default: |
'neb'
|
a string describing the task to be performed:
'neb',
'smd'
|
| restart_mode |
CHARACTER |
| Default: |
'from_scratch'
|
'from_scratch' : from scratch
'restart' : from previous interrupted run
|
| nstep_path |
INTEGER |
| Default: |
1
|
number of ionic + electronic steps
|
| num_of_images |
INTEGER |
| Default: |
0
|
Number of points used to discretize the path
(it must be larger than 3).
|
| 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.
|
| 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
|
| 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).
|
| temp_req |
REAL |
| Default: |
0.D0 Kelvin
|
Temperature used for the langevin dynamics of the string.
|
| 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.
|
|
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.
|
| 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.
|
| 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"
|
| 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.
|
|
|
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.
|
|
|
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