Neutral excitation densityfunctional theory: an efficient and variational firstprinciples method for simulating neutral excitations in molecules
Abstract
We introduce neutral excitation densityfunctional theory (XDFT), a computationally light, generally applicable, firstprinciples technique for calculating neutral electronic excitations. The concept is to generalise constrained density functional theory to free it from any assumptions about the spatial confinement of electrons and holes, but to maintain all the advantages of a variational method. The task of calculating the lowest excited state of a given symmetry is thereby simplified to one of performing a simple, lowcost sequence of coupled DFT calculations. We demonstrate the efficacy of the method by calculating the lowest singleparticle singlet and triplet excitation energies in the wellknown Thiel molecular test set, with results which are in good agreement with linearresponse timedependent density functional theory (LRTDDFT). Furthermore, we show that XDFT can successfully capture twoelectron excitations, in principle, offering a flexible approach to target specific effects beyond stateoftheart adiabatickernel LRTDDFT. Overall the method makes optical gaps and electronhole binding energies readily accessible at a computational cost and scaling comparable to that of standard density functional theory. Owing to its multiple qualities beneficial to highthroughput studies where the optical gap is of particular interest; namely broad applicability, low computational demand, and ease of implementation and automation, XDFT presents as a viable candidate for research within materials discovery and informatics frameworks.
 Publication:

Scientific Reports
 Pub Date:
 June 2020
 DOI:
 10.1038/s41598020652094
 arXiv:
 arXiv:1803.01421
 Bibcode:
 2020NatSR..10.8947R
 Keywords:

 Physics  Chemical Physics;
 Condensed Matter  Materials Science;
 Physics  Atomic and Molecular Clusters;
 Physics  Computational Physics;
 Quantum Physics
 EPrint:
 6 pages, 4 figures