Ab initio simulation of UV/vis absorption spectra for atmospheric modeling: method design for medium-sized molecules

Abstract

A procedure is presented to obtain accurate absorption cross-sections for dissociative excited states. The focus is the ability to approximate many vibrational degrees of freedom while maintaining a minimal computational time. The vibrational Hamiltonian for bound and unbound surfaces is solved within a discrete variable representation (DVR) framework. Properties and energies of excited states are computed using electron correlated singles and doubles equation-of-motion (EOM-CCSD) and similarity transformed equation-of-motion (STEOM-CCSD) methods as implemented in ACESII. The novelty of this procedure is that it is designed to work for medium-sized molecules (size limited by the choice of electronic structure method, not vibrational degrees of freedom) with one or more photodissociation pathways. The theoretical absorption cross-section of NaOH is presented as a small-scale example.

NOx Catalyzed Pathway of Stratospheric Ozone Depletion: A Coupled Cluster Investigation

“…EOMCC is similar to FSMRCC and was successfully used by Bartlett and co-workers for the simulation of UV/vis absorption spectra for atmospheric modeling. 29 All of the rate constants presented in the paper have been estimated from theoretically calculated barrier heights, using the Arrhenius equation. Pre-exponential factors are obtained from experimental data 43 All of the ROHF-CCSD(T) calculations on NO x catalyzed reactions have been performed using CFOUR.…”

“…Photodissociation energies are calculated using the Equation Of Motion Coupled Cluster (EOMCC) method. EOMCC is similar to FSMRCC and was successfully used by Bartlett and co-workers for the simulation of UV/vis absorption spectra for atmospheric modeling …”

Similarity transformed coupled cluster response (ST-CCR) theory - A time-dependent similarity transformed equation-of-motion coupled cluster (STEOM-CC) approach

“…(34) and (35)] are obtained by satisfying Eqs. (36) and (37). Therefore, the single-excitation block of G is practically decoupled from the double-and triple-excitation blocks.…”

“…STEOM-CC introduced by Nooijen and Bartlett 19,20 is an effective and accurate method for calculating transition energies. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] STEOM-CC can be viewed as an intermediate approach between FSCC [37][38][39][40][41][42][43][44] and equation-of-motion coupled cluster (EOM-CC). [45][46][47][48][49] The starting point of these three TID schemes [ Fig.…”