Strain-modulated electronic structure and interfacial dipole effects in HfS2/MgCl2 van der Waals heterostructure: A first-principles study

Van der Waals heterostructures (vdWHs) assembled from two-dimensional (2D) materials provide a versatile platform for tailoring electronic, optical, and catalytic properties at the atomic scale. In this work, we employ first-principles calculations to investigate the structural, electronic, optical, piezoelectric, and electrocatalytic properties of a HfS 2 /MgCl 2 vdWH. The heterostructure is thermodynamically stable and exhibits a type-I band alignment with an indirect HSE06 bandgap of 1.84 eV. Strong and nearly isotropic in-plane optical absorption (~16%) is observed in the visible region. The electron mobility reaches 1170 cm 2 ·V -1 ·s -1 along the x-axis, indicating pronounced transport anisotropy. A finite in-plane piezoelectric coefficient (e 11 = 0.067 × 10 -10 C/m) is also predicted, originating from the broken centrosymmetry of the structure. Interfacial charge redistribution induces a built-in dipole and a high work function of 6.23 eV. Additionally, the OER energetics are analyzed using the computational hydrogen electrode model, identifying the O⁎ → OOH⁎ step as the potential-determining step with a residual free-energy barrier of ~0.52 eV at the equilibrium potential (U = 1.23 V). Under ±10% uniaxial and biaxial strain, the bandgap is widely tunable from 0.25 to 2.59 eV, and the band-edge positions are strongly modulated, which is relevant for optoelectronic and photocatalytic considerations. These results suggest that HfS 2 /MgCl 2 is a multifunctional platform for strain-engineered optoelectronic and piezoelectric functionalities, with insights into interfacial electrocatalytic energetics. • Bandgap is tunable from 0.25 to 2.59 eV via uniaxial or biaxial strain. • Charge redistribution induces a dipole and a high work function of 6.23 eV. • Anisotropic electron mobility reaches 1170 cm2·V -1 ·s -1 along the x-direction. • The heterostructure shows intrinsic OER selectivity with a ~0.52 eV residual barrier at 1.23 V. • Strain tunes band-edge positions through dipole-mediated interfacial coupling.