Dietmar Heidrich’s research while affiliated with Leipzig University and other places

... These types of automatic propagation methods are especially useful when the phase space on which the wave function propagates is difficult to predict beforehand. 34 On the other hand, various types of reaction paths 35 including classical/semiclassical trajectories are often profitable to characterize the mechanisms of chemical reactions and are put to practical use in quantum dynamics simulations as references or indicators. Among trajectory-guided methods, 36−41 the multiconfigurational Ehrenfest (MCE) method 39−41 has been developed as a technique to simulate electronically nonadiabatic dynamics in multidimensional systems. ...

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A Structure-Based Gaussian Expansion for Quantum Reaction Dynamics in Molecules: Application to Hydrogen Tunneling in Malonaldehyde

... The once abstract notions of fractal space and time now appear naturally and inevitable in chaotic dynamic systems, c.f. Shlesinger et al. [70], and there is a chance for a new insight into the dynamics of chemical systems. This insight is needed as the concept of reaction path, as discussed above, seems to be a somewhat artificial chemical instrument presently, c.f. Heidrich [292], encountering troubles with formulation of the theory of thermally activated crossing of a potential energy barrier. However, despite the great utility of the concept of renewals, one may feel uneasy with the way one conjectures presently on the timescale dependence of the dispersion parameter ␤ in Kohlrauschs' relaxation function, c.f. equation (21). ...

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Developments in dispersive kinetics

... However, up to [23], the procedure for the calculation of the gradient extremal has required some expansive third derivatives of the surface [30]. Further, there are many additional solution curves and turning points [13,20,23]. Usually, however, one needs only the valley path from minimum to saddle point. ...

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A Valley Following Method

... In the electrophilic attack on aromatic compounds face cationization plays an important role in the discussion of possible reaction paths. Li § Na + etc. form minima on the PES in the face arrangement (centrosymmetrical association) [16, 17], but cations like H § CH3 ~, F § etc. form unfavourable structures which represent typical P-SP2 [16,181920. Face protonated pyrrole, which cannot be localized by modifications of method A but by methods B and C, shows two strong d-modes vii =2700i cm -1, and u~ = 2834i cm -1 both indicating a shift of the central proton to the periphery of the ring system (Fig. 1,Table 1). ...

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Saddle points of index 2 on potential energy surfaces and their role in theoretical reactivity investigations

... In all CI calculations, the MO active space included all p, p* and n type orbitals. The solvation energy was evaluated within the virtual charge model, using a slightly simplified version of the formula proposed by Heidrich et al. [29] E sol 0( 1 ...

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Rotamerism and electronic spectra of aza-derivatives of stilbene and diphenylbutadiene. A combined experimental and theoretical study

... Extended and repeated computational work on the energy profile of the 1,2-hydride (or 1,2-proton) shifts along the rim of the protonated benzene ring has been carried out decades ago (Kuck, 1990a(Kuck, , 2005b and till to date (see below). As far as the gaseous tautomeric toluenium ions are concerned, the order of stability elucidated early by ICR measurements by Hehre and his associates in 1976 (Devlin et al., 1976) was found to match well with that obtained by calculations that also appeared, starting even earlier (Isaacs & Cvitas, 1971;Devlin et al., 1976;Heidrich, Grimmer, & Sommer, 1976). Since then and following Dewar's AM1 semiempirical work published in 1986 (Dewar & Dieter, 1986), numerous further computational studies have accompanied experimental investigations. ...

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TOLUENIUM AND OTHER GASEOUS METHYLBENZENIUM IONS: COMPLEX INTERPLAY OF PROTONATED ARENES AND CYCLO‐OLEFINS

... The considerable success of quantum chemistry in predicting the ethyl cation structure in the gas phase was connected with the quantum chemical ®ndings that only correlated levels of theory are able to give correct predictions for structures of carbocations. Gradient procedures of geometry optimization and vibrational analyses were ®rst used to identify the stationary structures 1, 2 in 1976 [2,4]. These calculations used the fact that certain semi-empirical methods could reproduce the classical±nonclassical energy difference found by correlated ab initio methods. ...

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Exploring the potential energy surface of the ethyl cation by new procedures

... This event is called the bond breaking point (BBP) [3]. In n dimensions, the Det(H) = 0 manifold crosses the manifold of the valley-ridge inflection points (VRI) anywhere on the PES [14,[16][17][18][19] which play an important role in the theory of NT. On our 2-dimensional PES, a singular NT meets the VRI point. ...

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To a mechanical model of synthetic catch-bonds

... The reaction we investigated is the identity reaction of the monosubstitutedbenzene molecule reacting with hydrogen fluoride using BF 3 as the catalyst in the gas phase (Scheme 2). Following the literature, 38,39 we represented the catalyst by one BF 3 molecule, and the reactant complex consisting of one monosubstituted benzene ring with one hydrogen fluoride (HF) and one BF 3 . The QST2 technique was employed to obtain the optimized transition state structure of the reaction. ...

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Computational Study of Chemical Reactivity Using Information-Theoretic Quantities from Density Functional Reactivity Theory for Electrophilic Aromatic Substitution Reactions

... Over the past four decades, the small homogeneous (HX)m cyclic clusters (where m = 3-6 when X = F and Cl, and m = 3-5 when X = Br and I) have been characterized, and a number of studies have probed the cooperative effects of hydrogen bonding in these systems. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The enhanced attractive interactions in (HX)m cyclic clusters are evident through their larger dissociation energies (De) per hydrogen bond compared to the corresponding HX dimers. [38][39][40][41][42] Numerous studies have reported the De of homogeneous (HX) 2 structures. ...

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Systematic characterization of the homogeneous and heterogeneous hydrogen halide dimers