HMC simulations of electron-phonon systems

An implementation of Hybrid Monte Carlo (HMC) simulations for organic molecular semiconductors and similar electron-phonon systems. The code uses highly efficient Fourier acceleration (FA). Transient localisation (TL) simulations are supported, too.

This repository contains the code required to reproduce the results presented in "First-principle quantum Monte-Carlo study of charge carrier mobility in organic molecular semiconductors", arXiv:2312.14914 [cond-mat.mtrl-sci] by Johann Ostmeyer, Tahereh Nematiaram, Alessandro Troisi, Pavel Buividovich.

For questions concerning the code contact ostmeyer@hiskp.uni-bonn.de.

Implementation

The entire simulations are implemented in C (located in the simulation directory).

Compile

The code depends on Lapacke and FFTW3. Make sure you have recent installations available before you proceed.

After adjusting the Makefile according to your needs (possibly switching to another compiler), simply type make to compile all the C files.

Run Code

Adjust the input.txt file (current default simulates Rubrene at room temperature using HMC with FA) according to the next subsection. Alternatively, create a new file with the relevant input parameters. Then, for HMC simulations, execute:

./organic_main input.txt results.csv corr.csv

Scalar results will be written to results.csv (or any other file provided as a second argument). The Euclidean correlator is written to corr.csv. See organic_hmc.c and comments therein for details.

For TL simulations execute:

./organic_main input.txt results.csv greens.bin
./organic_conv greens.bin smear.txt greens_smeared.csv corr_smeared.csv

Again, scalar results are written to results.csv. In addition, binned Greens function values will be written to greens.bin in binary format. They are analysed by the organic_conv execution where, following the instructions in smear.txt, the Greens function is convoluted with a smearing kernel for the optical conductivity in greens_smeared.csv and transformed to Euclidean time in corr_smeared.csv. See organic_conv.c and comments therein for details.

Input file

The input file is structured as follows (comments after the # are for this README only and should not be added into the actual input file):

L1 L2		# spatial geometry in 2D
Nt		# number of (Euclidean) time slices for HMC / number of Greens function bins for TL
beta		# inverse temperature
J1 J2 J3	# J_a hopping amplitudes on triangular lattice
l1 l2 l3	# lambda_a hopping amplitude fluctuations
mu0		# reduced chemical potential
omega0		# phonon frequency
Nmd traj	# molecular dynamics steps, trajectory length in HMC (traj=0 sets default, optimal for FA) / ignored in TL
therm		# thermalisation steps / ignored in TL
N freq		# number of simulated trajectories, measurement frequency
a1 a2		# 1st unit cell vector in 2D
b1 b2		# 2nd unit cell vector in 2D
flavors		# fermionic flavors
# more flags... (e.g. STATIC_DISORDER for TL simulations)
# see organic_flags.c for options

For TL simulations an additional smear.txt file is needed:

beta Nt		# inverse temperature, number of (Euclidean) time slices for correlator output
w1		# any number of kernel widths for the smearing
w2
...

Data

The data used in the paper will gladly be provided upon request.

Stable Releases

v1.0.2 initial publication after the preprint, compatible with arXiv version v2.