Predictive Model of Charge Mobilities in Organic Semiconductor Small Molecules with Force-Matched Potentials

Abstract

Charge mobility of crystalline organic semiconductors (OSC) is limited by local dynamic disorder. Recently, the charge mobility for several high mobility OSCs, including TIPS-pentacene, were accurately predicted from a density functional theory (DFT) simulation constrained by the crystal structure and the inelastic neutron scattering spectrum, which provide direct measures of the structure and the dynamic disorder in the length scale and energy range of interest. However, the computational expense required for calculating all of the atomic and molecular forces is prohibitive. Here we demonstrate the use of density functional tight binding (DFTB), a semiempirical quantum mechanical method that is 2 to 3 orders of magnitude more efficient than DFT. We show that force matching a many-body interaction potential to DFT derived forces yields highly accurate DFTB models capable of reproducing the low-frequency intricacies of experimental inelastic neutron scattering (INS) spectra and accurately predicting charge mobility. We subsequently predicted charge mobilities from our DFTB model of a number of previously unstudied structural analogues to TIPS-pentacene using dynamic disorder from DFTB and transient localization theory. The approach we establish here could provide a truly rapid simulation pathway for accurate materials properties prediction, in our vision applied to new OSCs with tailored properties.

Semi-Automated Creation of Density Functional Tight Binding Models through Leveraging Chebyshev Polynomial-Based Force Fields

“…Inclusion of configurational total energies generally resulted in minimal impact on quality of the E Rep fit and was thus excluded from our training data, similar to previous efforts. 56,57 This results in the following objective function:…”

High-throughput virtual screening for organic electronics: a comparative study of alternative strategies

“…284,285 However, the calculation of this parameter is known to be computationally very demanding. Recent calculations of nonlocal electron-phonon couplings on one 268 or few 286,287 molecules required millions of CPU hours 288 for state-of-the-art methods (i.e. not suitable for HTVS) while computationally inexpensive empirical force fields yield inaccurate results as they are not parameterised to reproduce low-frequency phonons.…”

Semi-Automated Creation of Density Functional Tight Binding Models Through Leveraging Chebyshev Polynomial-based Force Fields

“…It's parameters are usually fit to reproduce DFT or experimental data, and it can be either pair-wise 22,24 or contain multi-center interactions. 25,26,63,64 All DFTB calculations discussed within this work were performed with the DFTB+ code, 56,57 using self-consistent charges (SCC) 53 and charge convergence criteria of 2.72×10 −5 eV (10 −6 au). Inclusion of an external van der Waals correction 65,66 is beyond the scope of our present study.…”

“…For this section of our study, we used a constant ChIMES 2-body polynomial order of 12 and a 3-body order of 8, similar to previous work. 63,64 All optimization discussed in here were performed with the LASSO/LARS algorithm with regularization of 10 −3 (see Section 3.5 for details). In doing so, we are able to rapidly create a reasonable E Rep for our models, allowing us to assess the effects of different values of R T i ψ and R T i n independently.…”