Ground-to-excited derivative couplings for the density functional-based tight-binding method: semi-local and long-range corrected formulations

Niehaus, Thomas A.

doi:10.1007/s00214-021-02735-y

Cited by 6 publications

(3 citation statements)

References 71 publications

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“…In principle, the treatment of different spin-states is possible at semiempirical quantum mechanical (SQM) levels of theory. , SQM methods are typically up to several orders of magnitude less expensive than high-level multireference treatments but still provide an excellent computational cost/accuracy ratio. The majority of work on MECI identification with SQM methods was conducted by the group of Thiel et al, − mainly based on the orthogonalization correction methods (OM x ). , Other studies have focused on time-dependent and spin-flip variants of the semiempirical density functional tight-binding methods. − …”

Section: Introductionmentioning

confidence: 99%

Fast Screening of Minimum Energy Crossing Points with Semiempirical Tight-Binding Methods

Pracht

Bannwarth

2022

J. Chem. Theory Comput.

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The investigation of photochemical processes is a highly active field in computational chemistry. One research direction is the automated exploration and identification of minimum energy conical intersection (MECI) geometries. However, due to the immense technical effort required to calculate nonadiabatic potential energy landscapes, the routine application of such computational protocols is severely limited. In this study, we will discuss the prospect of combining adiabatic potential energy surfaces from semiempirical quantum mechanical calculations with specialized confinement potential and metadynamics simulations to identify S0/T1 minimum energy crossing point (MECP) geometries. It is shown that MECPs calculated at the GFN2-xTB level can provide suitable approximations to high-level S0/S1 ab initio conical intersection geometries at a fraction of the computational cost. Reference MECIs of benzene are studied to illustrate the basic concept. An example application of the presented protocol is demonstrated for a set of photoswitch molecules.

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Section: Introductionmentioning

confidence: 99%

Fast Screening of Minimum Energy Crossing Points with Semiempirical Tight-Binding Methods

Pracht

Bannwarth

2022

J. Chem. Theory Comput.

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“…24,59,60 Semi-empirical implementations have also been reported recently. 61,62 Out of a variety of formalisms for computing nonadiabatic couplings within TDDFT, 21,58,[63][64][65] the one that is conceptually and computationally simplest is the "pseudo-wavefunction" approach. 21,59,60 Working within the TDA, both for conceptual simplicity and for the practical reasons discussed above, one might write the wavefunction for the Kth excited state as a linear combination of singly-excited Slater determinants, as in the CIS method:…”

Section: Nonadiabatic (Derivative) Couplingsmentioning

confidence: 99%

Spin-Flip TDDFT for Photochemistry

Herbert

Mandal

2022

Preprint

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This chapter provides an overview of computational methods based on "spin-flip" (SF) modifications to time-dependent density functional theory (TDDFT), with specific focus on photochemical problems that require exploration of excited-state potential energy surfaces and which may access crossing regions (conical intersections or seams) between those surfaces. Although TDDFT is a widely-used method for computing vertical excitation energies and electronic absorption spectra, it suffers from certain pathologies in the description of conical intersections whenever the ground state is involved. These issues are resolved in SF-TDDFT, albeit at the expense of greater spin contamination that sometimes becomes problematic, and which has motivated the development of spin-complete extensions of TDDFT that produce spin-pure (or nearly spin pure) eigenstates. Following a general introduction to conical intersections and the theoretical description of photochemical phenomena, the formalism of SF-TDDFT is reviewed along with an overview of applications in which SF-TDDFT has been combined with trajectory surface hopping to simulate photochemical reactions. From a theoretical point of view, this work emphasizes how recent modifications to TDDFT, which were originally designed to overcome the aforementioned problems, have the effect of rendering the theory more and more ``wave function-like'', blurring the distinction between TDDFT and limited configuration interaction models.

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“…One limiting factor for the MECP calculation is the ability of theoretical models to simultaneously describe the different electronic states near the intersection. While typically associated with costly high level ab initio calculations, , application of much less costly semiempirical approaches has proved to perform well. − Within the derivative coupling vector-free treatment, large reduction of the computational cost is achieved in combination with semiempirical methods of the GFN n -xTB level, ,, which provide reasonable estimates of S 0 / S 1 MECIs via the S 0 / T 1 MECP. , However, as discussed previously, only lowest-energy solutions for a priori specified differences in the net α and β occupation can be enforced in this framework. In consequence, states that involve higher energetic electronic states, or simply holes in the net occupations, are inaccessible within the GFN n -xTB framework.…”

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confidence: 99%

Finding Excited-State Minimum Energy Crossing Points on a Budget: Non-Self-Consistent Tight-Binding Methods

Pracht

Bannwarth

2023

J. Phys. Chem. Lett.

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The automated exploration and identification of minimum energy conical intersections (MECIs) is a valuable computational strategy for the study of photochemical processes. Due to the immense computational effort involved in calculating non-adiabatic derivative coupling vectors, simplifications have been introduced focusing instead on minimum energy crossing points (MECPs), where promising attempts were made with semiempirical quantum mechanical methods. A simplified treatment for describing crossing points between almost arbitrary diabatic states based on a non-self-consistent extended tight-binding method, GFN0-xTB, is presented. Involving only a single diagonalization of the Hamiltonian, the method can provide energies and gradients for multiple electronic states, which can be used in a derivative coupling-vector-free scheme to calculate MECPs. By comparison with high-lying MECIs of benchmark systems, it is demonstrated that the identified geometries are good starting points for further MECI refinement with ab initio methods.

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Ground-to-excited derivative couplings for the density functional-based tight-binding method: semi-local and long-range corrected formulations

Cited by 6 publications

References 71 publications

Fast Screening of Minimum Energy Crossing Points with Semiempirical Tight-Binding Methods

Fast Screening of Minimum Energy Crossing Points with Semiempirical Tight-Binding Methods

Spin-Flip TDDFT for Photochemistry

Finding Excited-State Minimum Energy Crossing Points on a Budget: Non-Self-Consistent Tight-Binding Methods

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