V. A. Pushkarchuk

Theoretical study of hyperfine interactions and optically detected magnetic resonance spectra by simulation of the C291[NV]-H172 diamond cluster hosting nitrogen-vacancy center

Single nitrogen-vacancy (NV) centers in diamond coupled to neighboring nuclear spins are promising candidates for room-temperature applications in quantum information processing, quantum sensing and metrology. Here we report on a systematic density functional theory simulation of hyperfine coupling of the electronic spin of the NV center to individual 13C nuclear spins arbitrarily disposed in the H-terminated C291[NV]-H172 cluster hosting the NV center. For the ‘families’ of equivalent positions of the 13C atom in diamond lattices around the NV center we calculated hyperfine characteristics. For the first time the data are given for a system where the 13C atom is located on the NV center symmetry axis. Electron paramagnetic resonance transitions in the coupled electron–nuclear spin system 14NV-13C are analyzed as a function of the external magnetic field. Previously reported experimental data from Dreau et al (2012 Phys. Rev. B 85 134107) are described using simulated hyperfine coupling parameters.

Ab initio modeling of the electronic and spin properties of the [NV] centers in diamond nanocrystals

The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree-Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]− centers, hydrogen passivated (C38H42, C71H84, C86H78), and with a free (unpassivated) surface (C38, C71, C86). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogenpassivated diamond nanocrystals with [NV]− centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal.

Quantum registers based on single NV + n13C centers in diamond: I. The spin Hamiltonian method

Details of the application of the spin Hamiltonian method for studying spin characteristics of a quantum register that includes an electron spin S = 1 of a single NV center in the ground electronic state and nuclear spins I = 1/2 of several isotopic atoms 13C located at different lattice sites near the vacancy of the NV center. Two methods of finding the hyperfine interaction tensors for these NV + n13C spin systems are considered, one of which is based on the conventional electron spin resonance (ESR) method, while the other involves methods of quantum chemistry. The results of the latter method are compared with ESR data and with spectra of optically detected magnetic resonance (ODMR) and with the character of the modulation of the ODMR echo decay observed in single NV + n13C systems. This comparison shows that the ab initio modeling of the spin characteristics of diamond nanoclusters containing NV centers makes it possible to obtain quantitative spin characteristics of the quantum registers under study.

Quantum-chemical modeling of structural, electronic, and spin characteristics of NV centers in nanostructured diamond: Surface effect

The effect of the surface of diamond on atomic, electronic, and spin properties of diamond nanocrystals containing single nitrogen-vacancy defects ([NV]− centers) is studied. The surface was modeled with clusters C33H30[NV]−, C66H72[NV]−, which were constructed based on bulk clusters C33H36[NV]− and C69H84[NV]−, respectively. In all cases, clusters in the triplet state S = 1 are considered with the cluster charge being −1. The geometric structure of clusters is optimized using the principle of minimization of the total energy of the system; then, the electronic and spin characteristics of clusters are calculated by the density functional theory. The isotropic and anisotropic hyperfine interaction constants of the electron spin of the NV center with the nuclear spin of the nitrogen atom and 13C atoms located at different sites in the cluster are calculated. It is found that, in contrast to bulk clusters with [NV]-centers in which the spin density is mainly localized at the three carbon atoms that are the nearest neighbors of the vacancy of the center, upon arrangement of the NV center in the immediate proximity to the surface, the spin density is redistributed such that it is mainly localized at the three carbon atoms that are the nearest neighbors of the nitrogen atom of the center and at C atoms that form the first atomic layer of the (111) surface of the nanocrystal.

ELASTIC MODULES AND LOW-FREQUENCY OSCILLATIONS OF ISOLATED CARBON NANOTUBES

Institute for Nuclear Problems, BSU, Bobruiskaya 11, 220050 Minsk, Belarus Iinstitute of Physical Organic Chemistry NASB Surganova 13, 220072 Minsk, Belarus alexp@ifoch.bas-net.by Belarusian State University of Informatics and Radioelectronics P. Browka 6, 220013 Minsk, Belarus vadimka@vadimka.com Al-Balqa Applied University, P.O. Box 204,1Amman 11953, Jordan B.I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, 220072 Minsk, Belarus

Structure and magnetic properties of Saturn-shaped fullerenol complexes with ferrocene and nickelocene dicarboxylic acids: DFT simulation

Abstract DFT simulations of the electron and spin structure of fullerenol derivatives C60(OH)24·2Fe(C5H4COOH)2 and C60(OH)24·2Ni(C5H4COOH)2 have shown that these compounds form stable complexes with intermolecular hydrogen bonds. Calculated exchange coupling constants for the last complexes indicate that they can possess ferromagnetic properties. If this is true, then compounds will have a great potential for medical application as drug delivers under the control of external magnetic field.

Towards scalable quantum computers: nano-design and simulations of quantum register

Quantum information technology (QIT) is extremely fast developing area strongly connected with achievements in modern physics. We present a review of recent achievements in implementation of solid-state scalable quantum processors with special emphasize on diamond-based quantum hardware.

Modeling of electronic and spin structure of single NV centers in nanostructured diamond: influence of nanodiamond surface

Modeling of atomic structure and distribution of spin density for the NV center formed close to the surface (111) of nano-diamond has been carried out using quantum-chemical PM3 and DFT methods. The case is considered where the nitrogen atom of NV center is located in the near-surface atomic layer of a face (111). The relaxation of surface atoms relative to the initial position results in N atom to be shifted from the cluster center parallel to the <111> direction by 0.16Å, and C atoms belonging to the surface layer are also shifted parallel to the <111> direction to the center by 0.18Å. As this takes place, C-C and C-N distances between relaxed atoms decrease and a graphite-like structure is formed on a (111) crystal face. In the structure, the N atom and C atoms nearest to it lay practically in the same plane. The formed CN bond can be considered as one-and-a-half bond. It has been found that unlike the NV center in bulk diamond for which the spin density is located mainly on the carbon atoms, being nearest neighbors to the vacancy of the NV center, in the case of the NV center located in immediate proximity to the surface, there is a redistribution of spin density resulting in its major allocation in three C atoms, the nearest neighbors to the N atom, that form the first atomic layer of a surface (111) of nano-crystal.

DFT MODELING OF STRUCTURAL, ELECTRONIC AND SPIN PROPERTIES OF NICKEL–NITROGEN-CONTAINING (NE8) CENTER IN NANODIAMOND

Quantum chemical simulations have been carried out for the positively charged hydrogen-passivated cluster C33H24N4Ni +1 having a spin-doublet (S=1/2) ground state. After simulation of the relaxed structure of the clusters, calculations of electronic and spin properties were performed. It was shown that the spin density is localized mainly (80 %) at Ni atom and at the six atoms (two carbon and four nitrogen atoms) that are the nearest neighbors to the Ni atom. The isotropic and anisotropic hyperfine coupling constants for Ni isotope (I=3/2), as well as for isotopes N (I=1) and C (I=1/2) of the relaxed lattice were calculated. The found values show that the NE8 center with isotopic nickel can be perspective for future quantum information technological application.