共查询到20条相似文献,搜索用时 15 毫秒
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A method is described for deducing the molecular weight of a compound, the mass spectrom of which does not extend as far as the molecular weight, It is based upon the combination of fragment ions and restricted to limits determined by an approximate estimate of that weight. 相似文献
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J.G. Powles 《Chemical physics letters》1982,86(4):335-339
“Non-destructive” computer simulation techniques for evaluating the chemical potential of a fluid are discussed. A simple case is used to obtain explicit analytical expressions for the functions involved. This illustrates the physical content of the statistical-mechanical analysis and is useful in explaining puzzling behaviour and in evaluating data on more realistic models of fluids obtained in this way. 相似文献
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Using a multireferent MBPT method (CIPSI) the electronic affinity (EA) of F, CN and HCC is computed. Results show how UMP2 gives unbalanced truncation of the MP series, while ROMP2 has the correct (balanced) behaviour. The good agreement with the experimental EA found for some compounds is accidental and associated to an error compensation. The good agreement with the experimental data found for the ROMP2 and CIPSI EAs is analysed.This paper was presented at the International Conference on The Impact of Supercomputers on Chemistry, held at the University of London, London, UK, 13–16 April 1987 相似文献
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An improved version of the “marching-cube” method1 is proposed for molecular surface triangulation. This new algorithm involves fewer and simpler basic building blocks and avoids the artificial gaps of the original one. Moreover, to make it applicable to the boundary element method, the procedures for the protein cavity identification and triangle reduction are also presented. The triangulation procedure was tested by incorporating it into the boundary element method (BEM) to estimate the pKa values of subtilisin BPN′ and bovine trypsin inhibitor (BPTI). © 1995 by John Wiley & Sons, Inc. 相似文献
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The overlap multipole expansion procedure is utilized for the evaluation of the component of the electrostatic molecular potential of the B-DNA helix due to its sugar-phosphate backbone. The overall shape of the potential, its extension in space, the location of the minima and the differences in the values of the potential in particularly significant regions (minor and major grooves, vicinity of the phosphates) are indicated. The isopotential surfaces are practically cylindrical at distances larger than 15 Å from the helix axis but exhibit a more complex structure at shorter distances.This paper is dedicated to Professor H. Hartmann on the occasion of his 65th birthday. 相似文献
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The influence of a single and double helical DNA environment on the molecular electrostatic potentials at the C8 and amino sites of guanine and adenine are studied. The results are employed in a tentative explanation of the variation in binding sites of N-acetoxy-N-2-acetylaminofluorene with DNA, following whether the nucleic acid is in a native or denatured state. 相似文献
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A new method is presented for defining a smooth, triangulated analytic surface for biological molecules. The surface produced by the algorithm is well-suited for use with a recently developed polarizationcharge technique1 for the computation of the electrostatic potential of solvated molecules, and may also be used for calculations of molecular surface areas and volumes. The new method employs Connolly's definitions of contact, reentrant and saddle surface,2 but includes modifications that preclude the presence of self-interesting reentrant surface, and also insure a rigorous decomposition of contact regions into curvilinear finite elements. The triangulation algorithm may be used in conjunction with the electrostatic methods described previously to compute the electric potential of molecules of arbitrary shape in solution. Applications include the estimation of hydration enthalpies, computation of the electrostatic forces associated with solvation, estimation of interactions between separate charged species in solution, and computation of the three-dimensional form of the molecular electric potential. Test calculations are presented for a double-stranded dinucleotide, the polypeptide enkephalin, and the protein ferredoxin. 相似文献
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I. I. Gegusin 《International journal of quantum chemistry》1991,40(1):87-95
This paper continues Part I of this paper, referred to in the following as I. The construction of a basis set is explicitly presented. The special case of MT potential is considered, and the corresponding secular equation is shown to match exactly the one resulting from the well-known scattered wave method. Finally, the bound states of a molecule are obtained as the solutions of a real-valued matrix eigenvalue problem. 相似文献
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Robert E. Tuzun Donald W. Noid Bobby G. Sumpter 《Macromolecular theory and simulations》1996,5(4):771-788
By using two- and three-body internal coordinates and their derivatives as intermediates, it is possible to enormously simplify formulas for three- and four-body internal coordinates and their derivatives. Using this approach, simple formulas are presented for stretch (two-body), two types of bend (three-body), and wag and two types of torsion (four-body) internal coordinates and their first and second derivatives. The formulas are eminently suitable for economizing molecular dynamics and molecular mechanics calculations and normal coordinate analysis of complicated potential energy surfaces. Efficient methods for computing derivatives of entire potential energy terms, and in particular cross terms with switching functions, are presented. 相似文献
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A rigorous treatment of the local electric field is used to calculate effective molecular polarizabilities from optical data for naphthalene, anthracene, phenanthrene and bighenyl crystals. The principal axes of polarizability are typically 10° from the molecular axes, in accord with spectroscopic results. Various applications are outlined. 相似文献
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The problem of calculating the effective molecular polarizabilities and the local electric fields in molecular crystals is considered. It is shown that in a crystal with two or more anisotropic molecules per unit cell, these quantities cannot be found from the crystal structure and the dielectric tensor alone. 相似文献
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《Polyhedron》2005,24(16-17):2562-2567
Molecular magnets have been recently proposed as possible building blocks for a solid-state quantum computer. In order to substantiate and develop such a proposal, one needs to identify those molecules that are best suited for the qubit encoding and manipulation. Here, we focus on a heterometallic molecular ring, namely Cr7Ni, where the substitution of one Cr3+(S = 3/2) with Ni2+(S = 1) provides an extra spin to the otherwise compensated molecule. We show that its ground state consists in an S = 1/2 doublet, energetically well separated (Δ0/kB ∼ 13 K at zero magnetic field) from the first excited multiplet. This relatively large value of Δ0, together with the reduced mixing of the subspaces corresponding to different values of the total spin S, enables a safe encoding of the |0〉 and |1〉 states with the ground-state doublet, and allows to coherently rotate the effective S = 1/2 spin, while keeping the population loss to the excited states negligible. A further, intriguing challenge is represented by the implementation of the conditional dynamics (two-qubit gates). We present here preliminary characterization of molecular “Cr7Ni-dimers”, i.e., derivatives in which two Cr7Ni rings are linked with each other by means of delocalized aromatic amines. The resulting intercluster couplings are estimated to be ⩽1 K and are expected to be permanent, i.e., not tuneable during gating, as required by the standard approach to quantum computation. We discuss a computational scheme that allows in principle to overcome this limitation. The most relevant decoherence mechanisms for Cr7Ni and possible ways to reduce their effects are discussed as well. 相似文献
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Relativistic Dirac-Coulomb (DC) Hartree-Fock calculations are employed to obtain the analytic electric field gradient (EFG) on the antimony nucleus in the SbN, SbP, SbF, and SbCl molecules. The electronic correlation contribution to the EFGs is included with the DC-CCSD(T) and DC-CCSD-T approaches, also in the four-component framework, using a finite-difference method. The total EFG results, along with the experimental nuclear quadrupole coupling constants from microwave spectroscopy, allow to derive the nuclear quadrupole moments of (121)Sb and (123)Sb, respectively, as -543(11) and -692(14) mb. 相似文献
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The molecular electrostatic potential of yeast tRNAPhe is calculated at sites bridging the anionic oxygens of each of the 76 phosphate groups of the molecule. A quantitative measure of the steric accessibility of the anionic oxygens of the phosphates toward a spherical cation is presented. Both the resulting potentials and accessibilities are discussed in terms of the molecular and electronic structure of tRNA. 相似文献