Quantum mechanics/molecular mechanics studies on the mechanistic photophysics of sunscreen oxybenzone in methanol solution

Abstract

Herein we have employed the QM(CASPT2//CASSCF)/MM method to explore the photophysical and photochemical mechanism of oxybenzone (OB) in methanol solution. Based on the optimized minima, conical intersections and crossing points,...

Quantum mechanics/molecular mechanics studies on mechanistic photophysics of cytosine aza-analogues: 2,4-diamino-1,3,5-triazine and 2-amino-1,3,5-triazine in aqueous solution

“…This strategy for system setup was adopted in many previous similar works. 33,[50][51][52][53][54][55] In MM minimizations and MD simulations, 2,4-DT and 2-AT are treated with the modified CHARMM22 force field and water molecules are described by the TIP3P model, respectively. [56][57][58] All MM computations are executed using the DL_POLY module of the CHEMSHELL3.5 package.…”

“…The state-average complete active space self-consistent field (SA-CASSCF) method over five roots with equal weights is taken as the QM electronic structure method to optimize the minima, minimum energy crossing points (MECPs) in and between the lowest singlet and triplet states, i.e., S 1 , S 2 , T 1 , T 2 , T 3 , and S 0 states. Note that MECPs involving electronic states of the same spin multiplicity are denoted as conical intersections, and those involving singlet and triplet states are singlet-triplet crossings (referred to as crossing points hereinafter, see our recent work 33,[50][51][52][53][54] ). The active space used for 2-AT is composed of three lone pair (n) orbitals localized on the nitrogen atoms of the triazine ring, one p orbital localized on the NH 2 group, and three p/p* orbitals delocalized over the triazine ring (referred to as CAS(14e,10o)).…”

“…, S 1 , S 2 , T 1 , T 2 , T 3 , and S 0 states. Note that MECPs involving electronic states of the same spin multiplicity are denoted as conical intersections, and those involving singlet and triplet states are singlet–triplet crossings (referred to as crossing points hereinafter, see our recent work 33,50–54 ). The active space used for 2-AT is composed of three lone pair (n) orbitals localized on the nitrogen atoms of the triazine ring, one π orbital localized on the NH 2 group, and three π/π* orbitals delocalized over the triazine ring (referred to as CAS(14e,10o)).…”

Quantum mechanics/molecular mechanics studies on the excited-state decay mechanisms of cytidine aza-analogues: 5-azacytidine and 2′-deoxy-5-azacytidine in aqueous solution

“…1), and a similar system setup strategy can be found in our previous works. 15,[26][27][28][29][30] In the computations of MM minimizations and MD simulations, the solute 5ACyd and 5AdCyd molecules are adopted with the prepared and modified CHARMM22 force field parameters and the solvent water molecules are described by the TIP3P model, respectively. [31][32][33] All MM computations are performed by means of the DL_POLY module of the CHEMSHELL3.5 package.…”

Quantum mechanics/molecular mechanics studies on excited state decay pathways of 5-azacytosine in aqueous solution

“…[67][68][69] Finally, we delete the frozen water molecules of the last MD snapshot to generate the starting structure for the subsequent QM/MM calculations and this strategy has been adopted in many similar works. 25,[70][71][72][73][74][75][76]…”