Pre-seeding diabatic anchors for reproducible direct-dynamics quantum photodissociation: an 8-state full-dimensional DD-vMCG study of CH2OO.

Direct-dynamics quantum simulations construct a potential-energy representation from electronic-structure data collected at selected nuclear geometries. When these data are accumulated during propagation, the resulting quasi-diabatic potentials can depend on the geometries encountered early in the calculation. We investigate whether supplying reference geometries in advance reduces this sensitivity in the photodissociation of CH2OO. A database containing the Franck-Condon reference and 97 additional entries along the mass- and frequency-weighted Q3 coordinate (dominated by O-O stretching) is compared with one initially confined to the Franck-Condon region, using the same direct-dynamics variational multi-configurational Gaussian (DD-vMCG) method. Both calculations include eight electronic states and all nine vibrational degrees of freedom at the SA-CASSCF(10e,8o)/6-31G(d,p) level, with production databases of approximately 5000 points. Along the sampled path, informed sampling produces smoother diagonal quasi-diabatic potentials and more clearly ordered changes in electronic-state composition. Both workflows show O-O extension, but the informed-sampling calculation retains population in the initially excited adiabatic state, S2, for longer before rapid multistate redistribution. These results identify database initialisation as a practical influence on the Hamiltonian representation and its predicted population dynamics. The state correlations support provisional assignments of the photodissociation channels, while quantitative branching ratios require further convergence and channel-resolved flux analysis.