Ring currents in condensed ring systems

Anusooya, Y.; Chakrabarti, Aparna; Pati, Swapan K.; Ramasesha, S.

doi:10.1002/(sici)1097-461x(1998)70:3<503::aid-qua6>3.0.co;2-y

Cited by 49 publications

(19 citation statements)

References 23 publications

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“…Purely -electronic PPP results for naphthalene, anthracene, and phenanthrene follow the same trends, but differ in the relative magnitudes for inner and outer rings. 35 Bonds shared between two rings can have opposite ring currents, as discussed by Fowler et al, 36 who calculate current-density maps in various polycyclic aromatics. These few examples underscore the diversity of molecular systems, both in composition and structure, while quantum cell models focus on the common features of conjugation.…”

Section: Discussionmentioning

confidence: 99%

Ring currents and charge stiffness in molecular and extended models of interacting fermions

Soos¹,

Pati²,

Pati³

2000

The Journal of Chemical Physics

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Articles you may be interested inMagnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phasesThe diamagnetic susceptibility of half-filled fermion models with Nϭ4nϩ2 sites is related to chemical shifts in molecules and charge stiffness in extended systems. The slow evolution of (N) with N in Hubbard models or spinless fermions indicates a small energy gap, as known from exact solutions of regular chains. A gap due to alternating transfer integrals ͑1Ϯ␦͒ suppresses for N␦ Ͼ1, but is a small correction for N␦Ͻ1. Exact ring currents N of Pariser-Parr-Pople ͑PPP͒ and Hubbard models are extended to Nϭ18 in D 18h symmetry. Hydrocarbon PPP parameters account for the anisotropy of proton shifts in 14 and 18 annulenes, for smaller shifts at larger N, and for larger shifts of anions with 4nϩ2 -electrons. Fermion models with arbitrary spin-independent interactions are shown to have vanishing for open boundary conditions ͑chains͒ at half filling or finite N. Diamagnetic currents in molecules require rings but are not sensitive to small bond-length variations, while an energy gap rather than topology enters in the charge stiffness of extended systems. Although formally identical, has different applications in finite and extended systems and its convergence with N can be rapid or very slow. Spin-charge separation reflects correlations rather than topology in half-filled Hubbard, PPP, and spinless fermion models; 4n and 4nϩ2 rings with oppositely signed show similar spin-charge separation with increasing correlations.

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Section: Discussionmentioning

confidence: 99%

Ring currents and charge stiffness in molecular and extended models of interacting fermions

Soos¹,

Pati²,

Pati³

2000

The Journal of Chemical Physics

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“…At the end of each iteration, one can calculate the properties of the targeted state [63]. The reduced many-body density matrix computed at each iteration can be used to calculate the static expectation values of any site operator or their products.…”

Section: Calculation Of Properties In the Dmrg Basismentioning

confidence: 99%

Exact and Approximate Theoretical Techniques for Quantum Magnetism in Low Dimensions

2003

Self Cite

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Quantum magnetism in low dimensions has been one of the central areas of theoretical research for many decades now. One of the key reasons for the long standing interest in this field has been the existence of simplified models, which serve as paradigms for understanding the role of strong interactions in many-electron systems. Although simple, these models quite often can not be solved exactly. In this review, we discuss a variety of analytical and numerical methods, which treat the system in a systematic and controlled manner. The central method employed in all the studies is the density matrix renormalization group (DMRG) method. This is supported by small scale numerical exact calculations, and by analytical methods using field theoretic techniques. We have considered a number of magnetic systems, from magnetic clusters to extended lattices, and have found some novel quantum ground states and low-energy elementary excitations. In some cases, we have also employed the finite-temperature DMRG method to accurately compute the low-temperature thermodynamic properties such as specific heat and magnetic susceptibility.

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“…The molecular structures of PAHs can have significant effects on their energetic, electronic, and magnetic properties . Let us take, for example, the two C 14 H 10 PAH isomers: (i) the first ionization potential (IP) of phenanthrene is higher by ∼39 kJ mol −1 than that of anthracene, (ii) phenanthrene has a larger HOMO–LUMO gap, and (iii) while the electronic ring currents in phenanthrene are localized mainly on the terminal rings, in anthracene they are localized mainly on the central ring . Similarly, of the five C 18 H 12 PAH isomers, triphenylene has the highest IP and the largest HOMO–LUMO gap .…”

Section: Introductionmentioning

confidence: 99%

How reliable is DFT in predicting relative energies of polycyclic aromatic hydrocarbon isomers? comparison of functionals from different rungs of jacob's ladder

Karton

2016

J Comput Chem

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Density functional theory (DFT) is the only quantum-chemical avenue for calculating thermochemical/kinetic properties of large polycyclic aromatic hydrocarbons (PAHs) such as graphene nanoflakes. Using CCSD(T)/CBS PAH isomerization energies, we find that all generalized gradient approximation (GGA) and meta GGA DFT functionals have severe difficulties in describing isomerization energies in PAHs. The poor performance of these functionals is demonstrated by the following root-mean-square deviations (RMSDs) obtained for a database of C H and C H isomerization energies. The RMSDs for the GGAs range between 6.0 (BP86-D3) and 23.0 (SOGGA11) and for the meta GGAs they range between 3.5 (MN12-L) and 11.9 (τ-HCTH) kJ mol . These functionals (including the dispersion-corrected methods) systematically and significantly underestimate the isomerization energies. A consequence of this behavior is that they all predict that chrysene (rather than triphenylene) is the most stable C H isomer. A general improvement in performance is observed along the rungs of Jacob's Ladder; however, only a handful of functionals from rung four give good performance for PAH isomerization energies. These include functionals with high percentages (40-50%) of exact Hartree-Fock exchange such as the hybrid GGA SOGGA11-X (RMSD = 1.7 kJ mol ) and the hybrid-meta GGA BMK (RMSD = 1.3 kJ mol ). Alternatively, the inclusion of lower percentages (20-30%) of exact exchange in conjunction with an empirical dispersion correction results in good performance. For example, the hybrid GGA PBE0-D3 attains an RMSD of 1.5 kJ mol , and the hybrid-meta GGAs PW6B95-D3 and B1B95-D3 result in RMSDs below 1 kJ mol . © 2016 Wiley Periodicals, Inc.

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Ring currents in condensed ring systems

Cited by 49 publications

References 23 publications

Ring currents and charge stiffness in molecular and extended models of interacting fermions

Ring currents and charge stiffness in molecular and extended models of interacting fermions

Exact and Approximate Theoretical Techniques for Quantum Magnetism in Low Dimensions

How reliable is DFT in predicting relative energies of polycyclic aromatic hydrocarbon isomers? comparison of functionals from different rungs of jacob's ladder

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