Quantum chemical calculation of electron ionization mass spectra for general organic and inorganic molecules

Abstract

The implementation of a novel tight-binding Hamiltonian within the QCEIMS program allows the first-principles based computation of EI mass spectra within a few hours for systems containing elements up to Z = 86.

Structure Optimisation of Large Transition‐Metal Complexes with Extended Tight‐Binding Methods

“…In particular,t he treatment of transition metals is limited or even impossible in many SQM methods.T his is contradicting the importance of transition metals in numerous and diverse areas of chemistry,partly involving very large or extended molecular or periodic systems.E xamples are supramolecular organometallic aggregates such as metalorganic polyhedra (MOPs) or macrocycles (MOMs), metalorganic frameworks (MOFs), and metal-containing biomolecules,s uch as metalloproteins or ac ombination to metal-biomolecule frameworks (MBioFs). [16,17] Thep otential field of application for efficient SQM methods is correspondingly large.However,universally applicable methods that are fully parameterised for transition metals are mostly limited to two method families,namely the already frequently used neglect of diatomic differential overlap (NDDO) based PMx (parametric method x)m ethods [4][5][6] and the recently introduced extended tight-binding methods GFNn-xTB, [1,2] (geometries,vibrational frequencies, and noncovalent interactions extended tight binding) from our laboratory.The robustness and quality of the GFNn-xTB methods has already been demonstrated in numerous applications with apredominant focus on organic chemistry.These applications include simulations of electron ionisation mass spectra, [18] fully automated computation of spin-spin-coupled nuclear resonance spectra, [19] including conformer-rotamer ensemble generation, atomic charge generation for the new D4 dispersion correction, [20,21] geometry optimisation of lanthanoid complexes, [22] automated determination of protonation sites, [23] pK a calculation in the SAMPL6 blind challenge, [24] metadynamics-based exploration of chemical compound conformation and reaction space, [25] and few studies on organometallic systems. [16,17] Thep otential field of application for efficient SQM methods is correspondingly large.However,universally applicable methods that are fully parameterised for transition metals are mostly limited to two method families,namely the already frequently used neglect of diatomic differential overlap (NDDO) based PMx (parametric method x)m ethods [4][5][6] and the recently introduced extended tight-binding methods GFNn-xTB, [1,2] (geometries,vibrational frequencies, and noncovalent interactions extended tight binding) from our laboratory.The robustness and quality of the GFNn-xTB methods has already been demonstrated in numerous applications with apredominant focus on organic chemistry.These applications include simulations of elect...…”

“…[8] Such compounds are not only highly interesting from af undamental chemistry point of view,b ut their unique properties also make them valuable for industrial technologies.T hey are used, for example,incatalysis, [9] for fuel storage, [10,11] as semi-conductor materials, [12] in ferroelectrics, [13] as filtration or selection materials,i nb iomedical applications such as bioimaging and sensing, [14] biomimetic mineralisation, [15] or as drug delivery systems. [16,17] Thep otential field of application for efficient SQM methods is correspondingly large.However,universally applicable methods that are fully parameterised for transition metals are mostly limited to two method families,namely the already frequently used neglect of diatomic differential overlap (NDDO) based PMx (parametric method x)m ethods [4][5][6] and the recently introduced extended tight-binding methods GFNn-xTB, [1,2] (geometries,vibrational frequencies, and noncovalent interactions extended tight binding) from our laboratory.The robustness and quality of the GFNn-xTB methods has already been demonstrated in numerous applications with apredominant focus on organic chemistry.These applications include simulations of electron ionisation mass spectra, [18] fully automated computation of spin-spin-coupled nuclear resonance spectra, [19] including conformer-rotamer ensemble generation, atomic charge generation for the new D4 dispersion correction, [20,21] geometry optimisation of lanthanoid complexes, [22] automated determination of protonation sites, [23] pK a calculation in the SAMPL6 blind challenge, [24] metadynamics-based exploration of chemical compound conformation and reaction space, [25] and few studies on organometallic systems. [26] Thefocus here is on demonstrating the quality of GFN2-xTB and its precursor GFN1-xTB for the structure optimisation of transition-metal complexes and in particular of very large organometallic systems,w hich are to date not possible otherwise.T he recently published GFN2-xTB approach features less empiricism, improved electrostatic interactions (multipole terms up to atomic dipolequadrupole interactions), as well as adensity (atomic charge)dependent London dispersion energy correction [27,28] at even slightly ...…”

Valence Photoionization of Thymine: Ionization Energies, Vibrational Structure, and Fragmentation Pathways from the Slow to the Ultrafast

“…Grimme and co-workersp ioneered the ab initio prediction of the fragmentation mechanism by predicting electron ionization mass spectra from first principles trajectory calculations. [36,37] They also appliedt his approacht op redict the electron ionization mass spectra of NABs, including thymine. [38] Aerosol flash vaporization has previously been used as as oft vaporization technique to bring involatile organics, [39,40] including vitamins [41] and oligopeptides, [42] into the gas phase.…”

Vollautomatisierte quantenchemische Berechnung von Spin‐Spin‐ gekoppelten magnetischen Kernspinresonanzspektren

“…Dies wird in den ersten drei Stufen des Protokolls erreicht, indem zuerst das CRE mithilfe der schnellen semiempirisch-quantenchemischen Tight-BindingMethode GFN-xTB,d ie im xtb-Code [17,18] implementiert ist, erzeugt wird. Die GFN-xTB-Methode wurde bereits erfolgreich auf verschiedene chemische Fragestellungen angewendet [19] und ist fürden vorgestellten Ansatz unverzichtbar. Um das CRE zu generieren, wurde hier ein mehrstufiger Algorithmus entwickelt, der sich aus dem Folgen der Normalmoden, der "genetischen" Strukturkreuzung und langen (1-2 ns) Moleküldynamik(MD)-Simulationen zusammensetzt (Details siehe SI).…”