A general purpose Fortran 90 electronic structure program for conjugated systems using Pariser–Parr–Pople model

A Fortran 90 Hartree–Fock program for one-dimensional periodic π-conjugated systems using Pariser–Parr–Pople model

“…Table 1: Variation of total energy (in eV) per unit cell (E cell ) of t-PA and PPP with the number of unit cells (N ) obtained using our earlier P-P-P code for finite systems(author?) [47], compared with the result for the infinite polymer obtained by the present code (last column).…”

“…In order to benchmark our code, first we use it to compute the total energy per unit cell (E cell ) for t-PA and the polymer PPP, and compare it with the results obtained using our earlier P-P-P code meant for finite systems(author?) [47], with the increasing system size. We also analyze the convergence of the total energy/cell with respect to the total number of k points (n k ) used for the BZ integration, number of cells considered for summation of exchange integral (n exc , cf.…”

“…[47] is tabulated in Table 1, while the E cell for the same systems in the infinite polymer limit, obtained by the present code ppp_bulk.x, is presented in the last column of the table. The t-PA was considered in its dimerized configuration, with the single (double) bond length of 1.45Å(1.35 Å), and the corresponding hopping matrix element to be 2.232 eV (2.568 eV).…”

“…Thus, in order to study their electronic structure and related properties, using the P-P-P model (or any other Hamiltonian), one needs to impose periodic boundary conditions, and perform infinite lattice sums to account for their infinite extent, which, our earlier computer program(author?) [47] lacks. With this aim in mind, we recently developed a P-P-P model-based computer program, which solves both the restricted HF (RHF) and the unrestricted HF (UHF) equations for one-dimensional periodic systems, and used it to study the electronic structure and optical properties of mono-layer and multilayer GNRs of various kinds(author?)…”

“…For finite π-conjugated systems, in our group, we have developed a general-purpose HF program employing the P-P-P model, which is available to anyone for scientific work(author?) [47]. However, GNRs and some π-conjugated polymers are believed to be quasi-onedimensional systems, which need to be studied in the infinite-length limit.…”