Fitting coupled potential energy surfaces for large systems: Method and construction of a 3-state representation for phenol photodissociation in the full 33 internal degrees of freedom using multireference configuration interaction determined data

Abstract

A recently reported algorithm for representing adiabatic states coupled by conical intersections using a quasi-diabatic state Hamiltonian in four and five atom systems is extended to treat nonadiabatic processes in considerably larger molecules. The method treats all internal degrees of freedom and uses electronic structure data from ab initio multireference configuration interaction wave functions with nuclear configuration selection based on quasi-classical surface hopping trajectories. The method is shown here to be able to treat ∼30 internal degrees of freedom including dissociative and large amplitude internal motion. Two procedures are introduced which are essential to the algorithm, a null space projector which removes basis functions from the fitting process until they are needed and a partial diagonalization technique which allows for automated, but accurate, treatment of the vicinity of extended seams of conical intersections of two or more states. These procedures are described in detail. The method is illustrated using the photodissociaton of phenol, C6H5OH(${\rm \tilde X}{}^{1} A^{\prime} $X̃1A′) + hv → C6H5OH($\tilde A{}^{1} A^{\prime} $Ã1A′, ${\rm \tilde B}{}^{\rm 1}{\rm A^{\prime \prime} }$B̃1A′′) → C6H5O(${\rm \tilde X}{}^2{\rm B}_1$X̃2B1, ${\rm \tilde A}{}^2{\rm B}_2$Ã2B2) + H as a test case. Ab initio electronic structure data for the 1,2,31A states of phenol, which are coupled by conical intersections, are obtained from multireference first order configuration interaction wave functions. The design of bases to simultaneously treat large amplitude motion and dissociation is described, as is the ability of the fitting procedure to smooth the irregularities in the electronic energies attributable to the orbital changes that are inherent to nonadiabatic processes.

Multistate, multichannel coupled diabatic state representations of adiabatic states coupled by conical intersections. CH2OH photodissociation

“…Instead, surface hopping trajectories based on Tully's fewest switches method, 28 as implemented in the ANT program, 29 are used to determine the set of nuclear configurations for which H d must accurately represent the electronic structure data if the nonadiabatic process at hand is to be well described. 21 We define the domain of definition as the subspace of nuclear coordinate space for which H d reliably reproduces the ab initio data. A procedure for its construction based on quasiclassical surface hopping trajectories has been described in Ref.…”

“…A procedure for its construction based on quasiclassical surface hopping trajectories has been described in Ref. 21 = −1500 cm −1 . As seen in detail below, this shift results in considerable improvement in the D 0 for producing CH 2 O, cis-HCOH, and trans-HCOH from ground state CH 2 OH with little impact on remaining structures, including those of the reported conical intersections, for which the biggest geometric change is ∼0.05 Å, in 1, 2 2 A conical intersections.…”

“…21 In other language, we determine a removable approximation 32 to the nonremovable ab initio determined…”

On the description of conical intersections—A continuous representation of the local topography of seams of conical intersection of three or more electronic states: A generalization of the two state result

“…(6) was introduced and carefully analyzed in our recent work describing the representation of adiabatic potential energy surfaces coupled by conical intersections. 28 Here we provide a concise recapitulation of that analysis (Eqs. (7a)- (16)) sufficient to explain the present procedure.…”

Putting David Craig’s Legacy to Work in Nanotechnology and Biotechnology

“…[116] Non-adiabatic reactions depicting failure of the Born-Oppenheimer approximation were similarly treated in 1932 by London, [117] with the more well known but more restricted treatment of Landau also appearing in that year. [11,12] Today diabatic models are widely used to depict most chemical processes including electron-transfer, [118][119][120][121] natural photosynthesis and organic photovoltaics, [122][123][124][125][126][127][128][129][130][131][132][133] chemical quantum computing, [134,135] racemization processes, [136,137] non-adiabatic photochemical reactions, [138][139][140][141][142][143][144][145][146][147][148] proton-transfer, hydrogen bonding, hydrogen-transfer, coupled electron-proton transfer reactions, general reactions, [149] and aromaticity. [150][151][152][153][154] An essential aspect of this modern pre-eminence is its connection with Hush's adiabatic theory of electron transfer.…”