Jahn-Teller Distortion and Multiple-spin-state Analysis of Single-atom Vacancy in Graphene-nano-ribbon

A single-atom vacancy defect and its array in graphene and graphite were considered to be one candidate carrying the room-temperature ferromagnetism. Applying density functional theory to a single-atom vacancy in graphene-nano-ribbon (GNR), a detailed relationship between the multiple-spin-state and the Jahn-Teller distortion was studied. An equilateral triangle of an initial vacancy having six unpaired electrons had distorted to isosceles triangle by the Jahn-Teller effect. Among capable spin-state of Sz=6/2, 4/2 and 2/2, the most stable one was Sz=2/2. Total energy was 15.6 kcal/mol lower (stable) than that of the initial one and a sum of spin density (magnetic moment) around one vacancy was 1.49 {\mu}B. Amazing result was obtained in case of Sz=4/2. Initial flat ribbon turned to three dimensionally curled one. There appears ferromagnetic spin distribution on GNR. Total energy was -15.5kcal/mol, which was very close to that of Sz=2/2. Such calculation suggested the coexistence of flat ribbon and curled ribbon by generating vacancies. Bi-layered AB stacked GNR was analyzed in case of {\alpha}-site vacancy and also \b{eta}-site one. The most stable spin state was Sz=2/2 in both cases. These distorted vacancy triangle show 60 degree clockwise rotation from beta- to alpha-site, which is consistent with several experimental observations by using a scanning tunneling microscope.Comment: 9 pages, 9 figures, 2 table

Graphene Molecule Compared With Fullerene C60 As Circumstellar Carbon Dust Of Planetary Nebula

It had been understood that astronomically observed infrared spectrum of carbon rich planetary nebula as like Tc 1 and Lin 49 comes from fullerene (C60). Also, it is well known that graphene is a raw material for synthesizing fullerene. This study seeks some capability of graphene based on the quantum-chemical DFT calculation. It was demonstrated that graphene plays major role rather than fullerene. We applied two astrophysical conditions, which are void creation by high speed proton and photo-ionization by the central star. Model molecule was ionized void-graphene (C23) having one carbon pentagon combined with hexagons. By molecular vibrational analysis, we could reproduce six major bands from 6 to 9 micrometer, large peak at 12.8, and largest peak at 19.0. Also, many minor bands could be reproduced from 6 to 38 micrometer. Also, deeply void induced molecules (C22) and (C21) could support observed bands.Comment: 9 pages, 7 figure

Design of Magnetic Graphene-ribbon for 100 Tera-bit/inch2 Information Storage Media

Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch2 class data storage media. Multiple spin state analysis was done based on the density function theory. A typical model was a super cell [C80H7] which having bare (radical) carbons on one side zigzag edge, whereas mono hydrogenated on another side. Optimizing atomic configuration, self consistent calculation demonstrated that a total energy of the highest spin state is more stable than that of lower one, which came from exchange coupling between carbons. This analysis suggested a capability of designing magnetic data track utilizing such chemically edge modified graphene ribbon. In order to increase areal magnetization density, bilayer and quadri-layer graphene-ribbon model were analyzed. Detailed calculation resulted that also the highest spin state is the most stable one. Multiplying the layer numbers is effective way to realize and enhance strong magnetism.Comment: 4 pages, 8 figure

Reproduction of Interstellar Infrared Spectrum of Reflection Nebula NGC2023 By A Hydrocarbon Pentagon-Hexagon Combined Molecule

Reflection Nebula NGC2023 shows specific interstellar infrared spectrum due to polycyclic aromatic hydrocarbon (PAH) in a wide wavelength range from 5 to 20 micrometer. By our previous quantum chemistry calculation, it was suggested that a molecule group having hydrocarbon pentagon-hexagon combined skeleton could reproduce ubiquitous interstellar infrared spectrum. In this paper, observed NGC2023 spectrum was compared in detail with such carrier candidates. First model molecule was di-cation (C23H12)2+ with two hydrocarbon pentagons combined with five hexagons. Observed strong infrared bands were 6.2, 7.7, 8.6, and 11.2 micrometer. Whereas, calculated strong peaks were 6.4, 7.5, 7.7, 8.5, and 11.2 micrometer. Observed weaker bands from 10 to 15 micrometer were 11.0, 12.0, 12.7, 13.5, and 14.2 micrometer, which were reproduced well by computed bands as 10.9, 12.0, 12.6, 13.6, and 14.0 micrometer. From 15 to 20 micrometer, observed 15.8, 16.4, 17.4, 17.8, and 19.0 micrometer were correlated with calculated 15.6, 16.5, 17.2, 18.2, and 18.8 micrometer. It should be noted that we could successfully reproduce interstellar infrared spectrum by applying a single molecule. Second model molecule was (C12H8)3+ with one pentagon combined with two hexagons. Again, observed strong bands at 6.2, 7.7, 8.6, 11.2 and 12.7 micrometer were successfully computed as 6.3, 7.4, 7.7, 8.6, 11.1, and 12.8 micrometer. It was concluded that by introducing hydrocarbon pentagon-hexagon combined ionized molecules, interstellar PAH oriented infrared spectrum could be successfully reproduced.Comment: 6 pages, 3 figures, 1 tabl

Astrochemical Evolution Step From Acenaphthylene C12H8 To Pure Carbon C12 Around A Herbig Ae Young Star

Astrochemical evolution step of polycyclic aromatic hydrocarbon (PAH) around a Herbig Ae young star was analyzed using the first principles quantum chemical calculation. For simplicity, model molecule was selected to be acenaphthylene (C12H8) with hydrocarbon one pentagon combined with two hexagons. In a protoplanetary disk, molecules are illuminated by high energy photon from the central star and ionized to be cation (C12H8)n+ . Calculation shows that from n=0 to 6, molecule keeps its polycyclic hydrocarbon configuration. Whereas, at ionization step n=7, there occurs dehydrogenation of (C12H8) to pure carbon (C12). Such polycyclic pure carbon (PPC) would be attacked again by photons. At a stage of eighth ionization (C12)8+, there occur decomposition to aliphatic carbon chains, C9, C2, and mono carbon C1. Infrared spectra (IR) of those steps were calculated to identify observed spectra . Carrier molecules of Herbig Ae star WW Vul and HD145263 were identified by a combination of (C12H8)2+ and (C12H8)1+. Also, IR of HD37357 could be explained by (C12H8)2+, (C12H8)3+, and (C12H8)1+. Pure carbon molecules play an important role in many stars. IR of HD37258 was analyzed by a mixture of pure carbon (C12)2+, hydrocarbon (C12H8)2+ and neutral (C12H8)0+. Also, complex spectrum of HD38120 was analyzed by (C12)2+, (C12H8)2+ and (C12H8)3+. Acenaphthylene related molecules are just a typical example. We should apply various size molecules to understand total view around a new born star.Comment: 12pages, 10figure

Stable Spin State Analysis of Fe, Co, Ni-modified Graphene-ribbon

Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch2 class data storage media. In order to increase the saturation magnetization, first principles DFT analysis was done for Fe, Co, Ni-modified zigzag edge graphene-ribbon. Typical unit cell is [C32H2Fe1], [C32H2Co1] and [C32H2Ni1] respectively. Most stable spin state was Sz=4/2 for Fe-modified case, whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Magnetic moment of Fe,Co, and Ni were 3.63, 2.49 and 1.26 {\mu}B, which can be explained by the Hund-rule considering charge donation to neighboring carbons. Band calculation shows half-metal like structure with a large band gap (in Co-case, 0.55eV) for up-spin, whereas very small gap (0.05eV) for down-spin, which will be useful for many featured application like information storage, spin filter and magneto-resistance devices. Dual layer Fe-modified ribbon shows a tube like curved structure, which may suggest a carbon nanotube creation by Fe catalyst.Comment: 5 pages, 9 figures, 2 table

Herbig Ae Young Star's Infrared Spectrum Identified By Hydrocarbon Pentagon-Hexagon Combined Molecules

Infrared spectrum (IR) of Herbig Ae young stars was reproduced and classified by hydrocarbon pentagon-hexagon combined molecules by the quantum chemical calculation. Observed IR list by B. Acke et al. was categorized to four classes. Among 53 Herbig Ae stars, 26 samples show featured IR pattern named Type-D, which shows common IR peaks at 6.2, 8.3, 9.2, 10.0, 11.3, 12.1, and 14.0 micrometer. Typical star is HD144432. Calculation on di-cation molecule (C12H8)2+ having hydrocarbon one pentagon and two hexagons shows best coincidence at 6.1, 8.2, 9.2, 9.9, 11.3, 12.2, and 14.1 micrometer. There are some variation in Type-D. Spectrum of HD37357 was explained by a mixture with di-cation (C12H8)2+ and tri-cation (C12H8)3+. Ubiquitously observed spectrum Type-B was observed in 12 samples of Acke's list. In case of HD85567, observed 16 peaks were precisely reproduced by a single molecule (C23H12)2+. There is a mixture case with Type-B and Type-D. Typical example was HD142527. In this study, we could identify hidden carrier molecules for all types of IR in Herbig Ae stars.Comment: 8 pages,6 figures, 1 tabl

Astronomical Creation of Cyclic-C3H2 and Chain-C3 Due to Interstellar Deep Photoionization

Astronomical evolution mechanism of small size polycyclic aromatic hydrocarbon (PAH) was analyzed using the first principles quantum-chemical calculation. Starting model molecule was benzene (C6H6), which would be transformed to (C5H5) due to carbon void created by interstellar high speed proton attack. In a protoplanetary disk around a young star, molecules would be illuminated by high energy photon and ionized to be cationic-(C5H5). Calculation shows that from neutral to tri-cation, molecule keeps original configuration. At a step of sixth cation, there occurs surprising creation of cyclic-C3H2, which is the smallest PAH. Astronomical cyclic-C3H2 had been identified by radio astronomy. Deep photoionization of cyclic-C3H2 brings successive molecular change. Neutral and mono-cation keep cyclic configuration. At a step of di-cation, molecule was transformed to aliphatic chain-C3H2. Finally, chain-C3H2 was decomposed to pure carbon chain-C3 and two hydrogen atoms. Calculated infrared spectrum of those molecules was applied to observed spectrum of Herbig Ae young stars. Observed infrared spectrum could be partially explained by small molecules. Meanwhile, excellent coincidence was obtained by applying a larger molecules as like (C23H12)2+ or (C12H8)2+. Infrared observation is suitable for larger molecules and radio astronomy for smaller asymmetric molecules. It should be noted that these molecules could be identified in a natural way introducing two astronomical phenomena, that is, void-induced molecular deformation and deep photoionization.Comment: 11 pages, 13 figures, 1 tabl

Categorize Interstellar Infrared Spectrum by Polycyclic Pure-Carbon-Molecule and Hydrocarbon-Molecule

By applying quantum chemical calculation, interstellar infrared spectrum was categorized to three classes. Type-A show unusual feature of strong peaks at 11.3,12.9, and 14.0 micrometer. Usually observed 6.2, 7.7, and 8.6 micrometer bands are weak or not recognized. Typical examples are NGC1316 and NGC4589. Such spectrum could be identified for the first time by pure carbon molecule (C23)2+ (dication) having two carbon pentagons combined with five hexagons. Calculated spectrum coincided well at 11.3, 13.0, and 14.0 micrometer. Also we could find more coincidence at 5.2, 5.6, 7.6, 8.8,10.6,15.7 and 17.2 micrometer. Type-B is ubiquitously observed IR, but show medium strength at 11.3 micrometer. Examples are NGC6946 and the red triangle nebula. Coronene modified PAH (C23H12)2+ show best coincidence for both wavelength and strength. Type-C is usualy observed one featuring very strong peak at 11.3 micrometer. Examples are NGC7023, NGC2023 and M17SW. One capable expanation of large 11.3 micrometer band is a mixture of Type-A and Type-B. Combination of polycyclic pure-carbon-molecule and hydrocarbon-molecule may give a variety of IR spectrum.Comment: 9 pages, 7 figure

Multiple spin state analysis of magnetic nano graphene

Recent experiments indicate room-temperature ferromagnetism in graphite-like materials. This paper offers multiple spin state analysis applied to asymmetric graphene molecule to find out mechanism of ferromagnetic nature. First principle density functional theory is applied to calculate spin density, energy and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C64H27, C56H24, C64H25, C56H22 and C64H23 show that in every molecule the highest spin state is the most stable one with over 3000 K energy difference with next spin state. This result suggests a stability of room temperature ferromagnetism in these molecules. In contrast, nitrogen substituted molecules like C59N5H22, C52N4H20, C61N3H22, C54N2H20 and C63N1H22 show opposite result that the lowest spin state is the most stable. Magnetic stability of graphene molecule can be explained by three key issues, that is, edge specified localized spin density, parallel spins exchange interaction inside of a molecule and atom position optimization depending on spin state. Those results will be applied to design a carbon-base ferro-magnet, an ultra high density 100 tera bit /inch2 class information storage and spintronic devices.Comment: 6 pages, 8 figure