A Simple Effective SCF Method for Computing Optical Gaps in Organic Chromophores

Abstract

Photoluminescence effects in organic chromophores are of significant importance and requires precise description of low lying excited states. In this communication, we put forward an alternative time‐independent DFT scheme for computing lowest single‐particle excitation energy, especially for singlet excited state. This adopts a recently developed “virial“‐theorem based model of singlet‐triplet splitting which requires a DFT calculation on closed shell ground state and a restricted open‐shell triplet excited state, followed by a simple 2e- integral evaluation. This produces vertical excitation energies in small molecules, linear and non‐linear polycyclic aromatic hydrocarbon and organic dyes in comparable accuracy to the TDDFT. We also explore the functional dependency of present method with three different functionals (B3LYP, wB97X and CAM‐B3LYP) for polyenes and linear acenes. A systematic comparison with literature value illustrates the validity and usefulness of the present scheme in determining optical gap with fair computational cost.

Recent Advances in Cartesian-Grid DFT in Atoms and Molecules

“…This section produces optical gaps generated from n → π* and π → π* transitions in selected molecules in 15 is a subset. Now, similar to our previous conclusion, these results are also comparable with TD-B3LYP energies; in fact, the ones with B2 are in better agreement (Roy et al, 2021). This reflects the basis set dependency of these quantities.…”

“…This reflects the basis set dependency of these quantities. It is also delineated by Roy et al (2021) that TD-B3LYP significantly underestimates the excitation energies from the current procedure.…”

“…The discrete Fourier transforms are incorporated from the FFTW3 package (Frigo and Johnson, 2005). The above features are implemented in the InDFT (Roy et al, 2019) program developed in our laboratory over the years, which has been employed in several practical applications in a series of articles (Roy, 2008a;Roy, 2008b;Roy, 2010a;Roy, 2010b;Roy, 2011;Ghosal et al, 2016;Ghosal et al, 2018;Ghosal et al, 2019;Mandal et al, 2019;Ghosal et al, 2021;Roy et al, 2021;Ghosal and Roy, 2022a;Ghosal and Roy, 2022b;Roy et al, 2022). At this point, this includes some of the frequently used, prominent XC functionals mentioned at relevant places in the article.…”

A real-time TDDFT scheme for strong-field interaction in Cartesian coordinate grid

“…The construction of various TD potentials in H dy s (r g ,t) within the adiabatic approximation at a given time can be calculated analogous to their time-independent counterpart, and the details have been well documented in our earlier works [33][34][35][36][37][38][39][40][41]; hence not repeated here. Here we need to consider only the TD potential arising from an electric field.…”

“…The corresponding TIKS orbitals form the AES which lies at the heart of our propagation scheme. A systematic grid optimization technique from [36][37][38][39][40][41], provides an optimal grid which would be the starting point of our RT-TDDFT calculations. It is well justified in terms of current propagation scheme.…”