# NEB via Socket-Communication¶

[Input: recipes/interfaces/ase/neb/sockets/]

Note

To enable socket-communication in DFTB+ the WITH_SOCKETS flag in the configuration file config.cmake must be set to TRUE, before starting the compilation process!

## Providing the input for DFTB+¶

The composition of the input is analogous to the explanations in Socket-Communication. DFTB+ is invoked with the Socket{} driver, along the usual specifications for the Slater-Koster files, assuming that they are stored in the top-level directory of the calculation (same folder as dftb_in.hsd). The name dftbplus of the temporary file, which is required for communication via the i-PI protocol, initially only serves as a placeholder and is later replaced by the Python script used to run the NEB calculation. The extended HSD format allows to override properties (cf. Geometry) that were set earlier and is well suited for this use case. This effort is being made to ensure that each image has its own calculator attached:

Geometry = GenFormat {
<<< "../../dummy.gen"
}

Driver = Socket {
File = "dftbplus"
Protocol = i-PI {}
MaxSteps = -1
Verbosity = 10
}

Hamiltonian = DFTB {
SCC = Yes
SCCTolerance = 1.0e-06

MaxAngularMomentum = {
H = "s"
N = "p"
}

SlaterKosterFiles = Type2FileNames {
Prefix = "../../slakos/"
Separator = "-"
Suffix = ".skf"
}
}

ParserOptions {
ParserVersion = 8
}


## Geometry¶

For the geometries used as the initial and final state, please refer to section NEB (File-IO): Geometry.

## Main script¶

In many respects, the script at hand is similar to that for File-IO calculations (cf. NEB (File-IO): Main script). Nevertheless, a slight modification is necessary:

Performing the NEB calculation requires setting up a folder structure so that the calculation of an image is carried out in a separate directory and is assigned to its own ASE calculator, while communicating via a separate UNIX socket or temporary file respectively. The Python script shown below is a suitable and simple implementation to run a calculation with NIMAGES as the number of intermediate images (in this case set to 13).

DFTBP_PATH specifies the path to the DFTB+ executable and HSD_INPUT the path to the input file discussed above (cf. Providing the input for DFTB+).

A list with the working directories for the DFTB+ calculations is then created and the input file is read. Method write_modhsd creates the separate subfolders for the different DFTB+ image calculations and copies the input file into the created directories. Using the capabilities of the extended HSD format, the filename dftbplus of the temporary communication file gets overwritten according to the corresponding image number.

A list of instantiated socket calculators is created and its elements attached to the single intermediate images. Sockets and clients are invoked and the calculators are closed after the calculations have been carried out:

import os
from subprocess import Popen
from ase.neb import NEB
from ase.optimize import BFGS
from ase.calculators.socketio import SocketIOCalculator

NIMAGES = 13

DFTBP_PATH = 'dftb+'
HSD_INPUT = 'dftb_in.hsd'
GEO_PATH = 'NH3_initial.gen'

def main():
'''Main driver routine.'''

write('dummy.gen', system, format='gen')

images = [initial]
images += [initial.copy() for ii in range(NIMAGES)]
images += [final]

neb = NEB(images)
neb.interpolate()

opt = BFGS(neb, trajectory='i2f.traj')

socketids = range(1, NIMAGES + 1)
wdirs = ['_calc/image_{:d}'.format(socket) for socket in socketids]
unixsockets = ['dftbplus_{:d}'.format(socket) for socket in socketids]

write_modhsd(socketids)

calcs = [SocketIOCalculator(log='socket.log', unixsocket=unixsocket)
for unixsocket in unixsockets]

for ii, calc in enumerate(calcs):
images[ii + 1].set_calculator(calc)

for cwd in wdirs:
Popen(DFTBP_PATH, cwd=cwd)

opt.run(fmax=1.00E-02)

for calc in calcs:
calc.close()

def write_modhsd(socketids):
'''Writes input files based on 'dftb_in.hsd' with modified unixsockets.

Args:
socketids (1darray): contains unixsocket identifier
'''

for socket in socketids:
path = '_calc/image_{:d}'.format(socket)
os.makedirs(path, exist_ok=True)

with open(path + '/dftb_in.hsd', 'w') as file:
driver = '  <<+ ../../dftb_in.hsd' + '\n\n' + \
'+Driver = +Socket ' + '{\n' + \
'    !File = "dftbplus_{:d}"'.format(socket) + '\n}'
file.write(driver)

if __name__ == "__main__":
main()


## Analysis¶

For a short introduction to the evaluation of the results, please consult the relevant section NEB (File-IO): Analysis.