Investigation of challenging spin systems using Monte Carlo configuration interaction and the density matrix renormalization group

Abstract

We investigate if a range of challenging spin systems can be described sufficiently well using Monte Carlo configuration interaction (MCCI) and the density matrix renormalization group (DMRG) in a way that heads toward a more "black box" approach. Experimental results and other computational methods are used for comparison. The gap between the lowest doublet and quartet state of methylidyne (CH) is first considered. We then look at a range of first-row transition metal monocarbonyls: MCO when M is titanium, vanadium, chromium, or manganese. For these MCO systems we also employ partially spin restricted open-shell coupled-cluster (RCCSD). We finally investigate the high-spin low-lying states of the iron dimer, its cation and its anion. The multireference character of these molecules is also considered. We find that these systems can be computationally challenging with close low-lying states and often multireference character. For this more straightforward application and for the basis sets considered, we generally find qualitative agreement between DMRG and MCCI. © 2017 Wiley Periodicals, Inc.

Molecular Photochemistry: Recent Developments in Theory

“…[37,[39][40][41][42][43] Further studies on spin-crossover systems have focused on the calculation of spin states in oxo-Mn(Salen), [44] Fe II porphin, [45] dinuclear Fe II compounds, [46] chloro-ligated iron(IV)-oxo porphyrin, [47] and metal monocarbonyl species. [48] Early studies of excited states with DMRG were concerned with the dissociation curves of diatomic molecules, [49][50][51] but genuine applications of photophysical and photochemical processes are slowly coming to light. Examples include the photochromic ring opening of spiropyran, [52] the low-energy spectrum of [2Fe-2S] and [4Fe-4S] clusters, [53] the low-lying singlet states of trans-polyenes up to C 20 H 22 , [54] the electronic structure of an aphthalene excimer, [55] singlet donor-acceptor copolymers for singlet fission applications, [56] photocyclizations, [57] the delayed fluorescence in carbenemetal amides, [58] and excitations in carotenoids.…”

“…Applications of this method are flourishing, again with a particular focus on transition‐metal complexes, for example the Cr 2 bonding problem, the Mn 4 CaO 5 cluster model of the oxygen evolution complex of photosystem II, or problems concerning spin energetics . Further studies on spin‐crossover systems have focused on the calculation of spin states in oxo‐Mn(Salen), Fe II porphin, dinuclear Fe II compounds, chloro‐ligated iron(IV)‐oxo porphyrin, and metal monocarbonyl species . Early studies of excited states with DMRG were concerned with the dissociation curves of diatomic molecules, but genuine applications of photophysical and photochemical processes are slowly coming to light.…”

Molekulare Photochemie: Moderne Entwicklungen in der theoretischen Chemie

“…[37,[39][40][41][42][43] Weitere Studien von Spin-Crossover-Systemen konzentrierten sich auf die Berechnung von Spin-Zuständen in Oxo-Mn(Salen), [44] Eisen(II)-Porphin, [45] zweikernigen Eisen(II)-Verbindungen, [46] Chloroeisen(IV)-Oxo-Porphyrin [47] und Metallmonocarbonylen. [48] ¾ltere Untersuchungen angeregter Zustände mit DMRG behandelten die Dissoziationskurven von zweiatomigen Molekülen, [49][50][51] aber die Anzahl aufwendigerer Studien von photophysikalischen und photochemischen Prozessen wächst stetig. Einige Beispiele sind die photochrome Ringçffnungsreaktion von Spiropyranen, [52] das niederenergetische Spektrum von [2Fe-2S]-und [4Fe-4S]-Clustern, [53] die niedrigliegenden Singulett-Zustände der trans-Polyene bis C 20 H 22 , [54] die Elektronenstruktur des Naphthalin-Excimers, [55] Singulett-Donor-Akzeptor-Copolymere fürS inglet-Fission-Anwendungen, [56] Photozyklisierungen, [57] die zeitverzçgerte Fluoreszenz in Carben-Metall-Amid-Verbindungen [58] und Anregungen in Carotenoiden.…”

“…Eine Vielzahl an Anwendungen wurde in den letzten Jahren veröffentlicht, insbesondere zur Beschreibung von Übergangsmetallkomplexen – beispielsweise bei der Cr 2 ‐Bindung, dem Mn 4 CaO 5 ‐Cluster‐Modell des sauerstoffproduzierenden Komplexes (“oxygen‐evolving complex”) von Photosystem II oder Komplexen mit ungeklärter Spin‐Energetik . Weitere Studien von Spin‐Crossover‐Systemen konzentrierten sich auf die Berechnung von Spin‐Zuständen in Oxo‐Mn(Salen), Eisen(II)‐Porphin, zweikernigen Eisen(II)‐Verbindungen, Chloroeisen(IV)‐Oxo‐Porphyrin und Metallmonocarbonylen . Ältere Untersuchungen angeregter Zustände mit DMRG behandelten die Dissoziationskurven von zweiatomigen Molekülen, aber die Anzahl aufwendigerer Studien von photophysikalischen und photochemischen Prozessen wächst stetig.…”