Accurate quantum chemical treatment of covalently bonded biomolecules using fragment-based approaches remains a major challenge as fragmenting across covalent bonds disrupts essential electron correlation and long-range polarization. Importantly, a few of the previously developed fragment-based methods can accurately and efficiently treat both noncovalently and covalently bonded molecular systems, highlighting a significant gap in the field. A key novelty of the grid-adapted many-body analysis (GAMA) framework is that it overcomes this limitation. Building on our earlier work establishing GAMA for noncovalent systems, we extend this framework to covalently bonded biomolecules and develop GAMA2, a fully automated protocol that integrates a simple grid-based fragmentation scheme, many-body expansion with overlapping fragments truncated at two-body order, and a multilayer low-level correction. Across diverse peptides, ranging from flexible bioactive motifs to structured 18-mer helixes, GAMA2 reproduces supersystem MP2/6-311G(d,p) energies with unsigned absolute errors of ∼0.01-4 kcal/mol for flexible small- and medium-size peptide systems using HF as a low level of theory and ∼2-5 kcal/mol for complicated helical-type peptide structures when using M06-2X/6-311G(d,p) as the low-level method, showing substantial improvement over HF using accurate DFT-based methods. In addition to this highly accurate results, GAMA2 also demonstrate a significant computational speedup with HF as a super system low-level method relative to the reference full MP2 calculation, establishing GAMA2 as a scalable, efficient, and systematically improvable route for correlated quantum chemical calculations on biomolecular systems.
Understanding the mechanisms of UV-induced degradation is crucial for enhancing the UV stability of perovskite solar cells. The UV-driven structural dynamics of CH3NH3PbI3 (MAPbI3) are investigated using real-time TDDFT simulations, revealing that under the electron and hole excitation, the distortion of the inorganic framework is primarily driven by the electron occupation of Pb-p and I-p antibonding states, whereas in the hole case, it is mainly governed by the direct cooling induced distortion. We also found that UV accelerates the rotation of MA+ molecules. Further, a BDO molecule is introduced as a passivant, which suppresses structural distortions and provides multiphonon channels to dissipate carrier cooling energy. Experimental results confirm the UV-protective role of BDO, with suppressed PbI2 formation and improved device stability. These results clarify the mechanism of UV-induced degradation in the MAPbI3 perovskite and further elucidate how passivation molecules enhance the UV stability.

