Effect of Charge Transfer and Solvation on X-Ray Absorption Near-Edge Spectra in Microsolvated Environment

Electron delocalization in microsolvated clusters can substantially modify the character of electronic states accessed after core excitation. In this work, the K-edge XANES spectra of [Al(H₂O)_n]³⁺, with n = 1-6 complexes, are examined using the fc-CVS-EOM-CCSD and CVS-ADC(2)-x methods. We evaluate the influence of progressive hydration within first- and second-shell configurations on the core-excited electronic structure. Systematic variations occur in spectral properties for excitations into valence-like 3s, 3p, 4s, and 3d states. The charge-transfer analysis of representative 1s → 3p transitions indicates changes in spatial distribution and degree of excited-electron delocalization. Our results demonstrate the selective dependence of solvation geometry on governing the Al K-edge spectral features and the comparative application of highly correlated wave function approaches providing a method-resolved picture of the underlying microsolvation effect.