A benchmark theoretical study of the electron affinities of benzene and linear acenes

Abstract

A benchmark theoretical determination of the electron affinities of benzene and linear oligoacenes ranging from naphthalene to hexacene is presented, using the principles of a focal point analysis. These energy differences have been obtained from a series of single-point calculations at the Hartree–Fock, second-, third-, and partial fourth-order Møller–Plesset (MP2, MP3, and MP4SDQ) levels and from coupled cluster calculations including single and double excitations (CCSD) as well as perturbative estimates of connected triple excitations [CCSD(T)], using basis sets of improving quality, containing up to 1386, 1350, 1824, 1992, 1630, and 1910 basis functions in the computations, respectively. Studies of the convergence properties of these energy differences as a function of the size of the basis set and order attained in electronic correlation enable a determination of the vertical electron affinities of the four larger terms of the oligoacene (C2+4nH2+2n) series within chemical accuracy (0.04eV). According to our best estimates, these amount to +0.28, +0.82, +1.21, and +1.47eV when n=3, 4, 5, and 6. Adiabatic electron affinities have been further calculated by incorporating corrections for zero-point vibrational energies and for geometrical relaxations. The same procedure was applied to determine the vertical electron affinities of benzene and naphthalene, which are found to be markedly negative (∼−1.53 and ∼−0.48eV, respectively). Highly quantitative insights into experiments employing electron transmission spectroscopy on these compounds were also amenable from such an approach, provided diffuse atomic functions are deliberately removed from the basis set, in order to enforce confinement in the molecular region and enable a determination of pseudoadiabatic electron affinities (with respect to the timescale of nuclear motions). Comparison was made with calculations employing density functional theory and especially designed models that exploit the integer discontinuity in the potential or incorporate a potential wall in the unrestricted Kohn–Sham orbital equation for the anion.

Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes

“…Consequently, the experimental singlet-triplet energy gaps (ST gaps) of n-acenes are only available up to pentacene [109][110][111][112]. On the theoretical side, since n-acenes belong to conjugated π-orbital systems, high-level ab initio multi-reference methods, such as the density matrix renormalization group (DMRG) algorithm [115,122], the variational twoelectron reduced density matrix (2-RDM) method [121,124], and other high-level methods [114,[118][119][120], are typically required to capture the essential strong static correlation effects.…”

“…Recently, linear n-acenes (C 4n+2 H 2n+4 ), containing n linearly fused benzene rings (see Figure 10), have attracted considerable interest in the research community owing to their promising electronic properties [20,21,[45][46][47][48][109][110][111][112][113][114][115][116][117][118][119][120][121][122][123][124]. The electronic properties of nacenes have been found to be highly dependent on the chain lengths.…”

Evaluating theGWApproximation with CCSD(T) for Charged Excitations Across the Oligoacenes

“…[2][3][4][5] In addition, acenes and other polycyclic aromatic hydrocarbons are abundant in the universe and their properties are of importance to astrophysics. Charged excitations, namely excited states associated with electron addition and removal, have been well-studied for acene molecules with a variety of computational approaches, including density functional theory (DFT), many-body perturbation theory (MBPT), and wavefunction-based quantum chemistry methods, [9][10][11] and hence constitute an excellent benchmark case for the development and refinement of methods. Additionally, aspects of charged excitations for acenes are still not entirely understood.…”

Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones

“…Before applying our B2π -PLYP model to compounds TAPQ-I and TAPQ-II, we have first calibrated it for singlemolecule magnitude of the pentacene molecule thanks to the existence of: (i) benchmark values of ionization potentials (IPs) and electron affinities (EAs) of oligoacenes; 39,40 and (ii) gas-phase experimental (UPS) value of (Ref. 41) for (more favored in this case) hole transport.…”