An improved version of NDDO method and its use in the study of bulk and surface properties of titania

Grebenyuk, A. G.; Zayets, Valentin A.; Gorlov, Yu. I.

doi:10.1007/bf02062220

Cited by 11 publications

(4 citation statements)

References 5 publications

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“…Quantum chemical calculations have been performed by using CLUSTER‐Z2 software based on the NDDO‐WF approximation 14–17 that allows HF self‐consistent field (SCF) calculations in the valence spd ‐basis (see detailed description of the calculation algorithm in Ref. 18).…”

Section: Model Calculationsmentioning

confidence: 99%

TUNCUR: Sequential codes for semiempirical quantum chemical calculations of tunneling current

Zayets

Sheka

2004

Int J of Quantum Chemistry

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Abstract. TUNCUR codes are aimed at a coherent calculation of both equilibrated structures and electronic properties of a substrate and STM tip altogether with the tunneling current between them in the framework of the same computational scheme. Both objects are modeled by atomic clusters. Quantum chemical calculations in TUNCUR codes are provided by sequential programs CLUSTER-Z1 and CLUSTER-Z2 that perform HF SCF calculations in the valence sp-and spd-basis, respectively. TUNCUR consist of three blocks that provide calculations of STM recordings in two modes of operation as well as computing local density of states. All calculations are performed over a grid of variable parameters. 1.IntroductionSince its invention [1], scanning tunneling microscopy (STM) has proven to be a powerful technique in viewing the surface structure of various systems with atomic resolution. In this technique, a small bias voltage V is applied between a sample and an "atomically sharp" tip, which yields a tunneling current I at typical tip-to-surface separation of several angstroms. Depending on the polarity of V, the tunneling occurs by transfer of electrons either from occupied states of the sample into unoccupied states of the tip, or from the tip to the sample. In the topographic mode (I=const mode) of STM operation [1], a feedback mechanism changes the tip-to-surface separation in order to keep the tunneling current constant. The STM image is given by recording the distance changes during a scan of the surface. In the alternative currentimaging mode (H=const mode) [2], an STM image is constituted by recording the tunneling current, as the tip scans the surface at a constant distance. No method has not been so powerful as SMT in observing a direct image of a surface on an atomic scale. However, numerous STM applications have revealed that STM does not necessarily image the atomic structure of the surface as a naïve ball model, but represents rather very delicate features of the surface electronic states (see [3,4] and references there in). That is why STM so greatly needs a thorough theoretical analysis and/or calculations to decode profound information from the experimental images, as no other conventional method of the surface characterization such as electron microscopy or low-energy electron diffraction.

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Section: Model Calculationsmentioning

confidence: 99%

TUNCUR: Sequential codes for semiempirical quantum chemical calculations of tunneling current

Zayets

Sheka

2004

Int J of Quantum Chemistry

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“…Another weighting factor technique for modifying C

_{italicAB}^{italicCoul}

within the weighting‐factors NDDO approximation (NDDO‐WF) was suggested in Ref. 12 and is realized in the CLUSTER‐Z2 software 15. In this case, expression (5) takes on the modified form where I ll ′ , as before, are given by (6), while the weighting factors F ll ′ which reduce the values of integrals assessed from (4), are defined as follows 12: Here, C l are atomic parameters (4 and 10 in the sp‐ and spd‐ basis, respectively).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…These techniques and appropriate programs are being used in widespread one‐processor program packages MOPAC 9, AMPAC 10, and CLUSTER‐Z1 11 for QC calculations of many‐atomic systems in the sp ‐basis. Ongoing to the spd ‐basis, the above techniques were modified within the NDDO‐WP 12, 13 and MNDO/d 14 approximations that led the foundation of program packages CLUSTER‐Z2 15 and MNDO94 16, respectively.…”

Section: Introductionmentioning

confidence: 99%

NANOPACK: Parallel codes for semiempirical quantum chemical calculations of large systems in the sp‐ and spd‐basis

Berzigiyarov

Zayets

Ginzburg

et al. 2002

Int J of Quantum Chemistry

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ABSTRACT:A parallel implementation of the conventionally used NDDO (MNDO, AM1, PM3, CLUSTER-Z1) and modified NDDO-WF (CLUSTER-Z2) techniques for semiempirical quantum chemical calculations of large molecular systems in the sp-and spd-basis, respectively, is described. The atom-pair distribution of data over processors forms the basis of the parallelization. The technological aspects of designing scalable parallel calculations on supercomputers (using ScaLAPACK and MPI libraries) are discussed. The scaling of individual algorithms and the entire package was carried out for model systems with 894, 1920, and 2014 atomic orbitals. The package speed-up provided by different multiprocessor systems involving a cluster of Intel PIII processors, Alpha-21264-processor-built machine MBC-1000M, and Cray-T3E is analyzed. The effect of computer characteristics on the package performance is discussed.

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“…In the present work the quantum chemical computations (by semiempirical MNDO, NDDO, AM1, and MNDO/H methods) of potential energy surface sections along the reaction pathway for some S E i and S N i(Si) reactions in a cluster approach have been performed. Also, the computations of quantum chemical indexes of organic molecules (maximum charges on the atoms, energies of frontier orbitals, bond dissociation energies, etc.)…”

Section: Introductionmentioning

confidence: 99%

Connection between Chemisorption Kinetics and Adsorption Equilibria of Organic Compounds on Oxide Surfaces

Bogillo¹,

Gun'ko²

1996

Langmuir

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Quantum chemical computations of potential energy surface sections along the reaction pathway for interaction of some molecules with silica surface OH groups in a cluster approach have been performed. Two minimums on the potential curves which are due to formation of linear hydrogen-bonded and following cyclic donor-acceptor complexes were observed prior to formation of the transition state for proton transfer in the cyclic complexes. Some tendencies between quantum chemical indexes of organic molecules and heats of the complex formation or chemisorption activation energies on the silica surface have been established.

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An improved version of NDDO method and its use in the study of bulk and surface properties of titania

Cited by 11 publications

References 5 publications

TUNCUR: Sequential codes for semiempirical quantum chemical calculations of tunneling current

TUNCUR: Sequential codes for semiempirical quantum chemical calculations of tunneling current

NANOPACK: Parallel codes for semiempirical quantum chemical calculations of large systems in the sp‐ and spd‐basis

Connection between Chemisorption Kinetics and Adsorption Equilibria of Organic Compounds on Oxide Surfaces

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