Electronic Structure and Visible-Light Response of a Phosphonate-Coordinated Tungsten Oxide (WO3) Model: A First-Principles Study

Abstract

The rational design of visible-light-active photocatalysts requires a detailed understanding of how local coordination environments modulate the electronic structure and key photocatalytic descriptors. In this work, we present a first-principles investigation of the electronic structure and optical properties of a tungsten–phosphonate metal–organic framework model using density functional theory. A minimal W–phosphonate cluster, consisting of a WO? unit coordinated by phosphonate groups, is adopted to capture the essential features of the W–O–P motif while maintaining computational tractability. Electronic structure calculations performed at the PBE level reveal a semiconducting character with a valence band dominated by ligand-derived O 2p states and a conduction band primarily composed of W 5d orbitals, indicative of ligand-to-metal charge transfer (LMCT) excitations. Hybrid HSE06 calculations yield an improved band gap of 1.92 eV and enable an accurate alignment of band edges with respect to the vacuum level and water redox potentials. The resulting band positions indicate a strong thermodynamic driving force for the hydrogen evolution reaction, while oxygen evolution is found to be marginally accessible. Time-dependent DFT calculations further demonstrate pronounced visible-light absorption, with an intense band centered at approximately 545 nm originating from LMCT transitions. Overall, this study elucidates the electronic and optical consequences of phosphonate coordination on tungsten-based frameworks and provides atomistic insights relevant for the rational design of visible-light-responsive photocatalysts.