1,615 research outputs found

    Using the local density approximation and the LYP, BLYP, and B3LYP functionals within Reference--State One--Particle Density--Matrix Theory

    Full text link
    For closed-shell systems, the local density approximation (LDA) and the LYP, BLYP, and B3LYP functionals are shown to be compatible with reference-state one-particle density-matrix theory, where this recently introduced formalism is based on Brueckner-orbital theory and an energy functional that includes exact exchange and a non-universal correlation-energy functional. The method is demonstrated to reduce to a density functional theory when the exchange-correlation energy-functional has a simplified form, i.e., its integrand contains only the coordinates of two electron, say r1 and r2, and it has a Dirac delta function -- delta(r1 - r2) -- as a factor. Since Brueckner and Hartree--Fock orbitals are often very similar, any local exchange functional that works well with Hartree--Fock theory is a reasonable approximation with reference-state one-particle density-matrix theory. The LDA approximation is also a reasonable approximation. However, the Colle--Salvetti correlation-energy functional, and the LYP variant, are not ideal for the method, since these are universal functionals. Nevertheless, they appear to provide reasonable approximations. The B3LYP functional is derived using a linear combination of two functionals: One is the BLYP functional; the other uses exact exchange and a correlation-energy functional from the LDA.Comment: 26 Pages, 0 figures, RevTeX 4, Submitted to Mol. Phy

    Self-Diffusion of a Polymer Chain in a Melt

    Full text link
    Self-diffusion of a polymer chain in a melt is studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account. Polymer chains, each of which consists of NN segments, are located on an LƗLƗLL \times L \times L simple cubic lattice under periodic boundary conditions, where each segment occupies 2Ɨ2Ɨ22 \times 2 \times 2 unit cells. The results for N=32,48,64,96,128,192,256,384N=32, 48, 64, 96, 128, 192, 256, 384 and 512 at the volume fraction Ļ•ā‰ƒ0.5\phi \simeq 0.5 are reported, where L=128L = 128 for Nā‰¤256N \leq 256 and L=192 for Nā‰„384N \geq 384. The NN-dependence of the self-diffusion constant DD is examined. Here, DD is estimated from the mean square displacements of the center of mass of a single polymer chain at the times larger than the longest relaxation time. From the data for N=256N = 256, 384 and 512, the apparent exponent xdx_{\rm d}, which describes the apparent power law dependence of DD on NN as DāˆNāˆ’xdD \propto N^{- x_{\rm d}}, is estimated as xdā‰ƒ2.4x_{\rm d} \simeq 2.4. The ratio DĻ„/D \tau / seems to be a constant for N=192,256,384N = 192, 256, 384 and 512, where Ļ„\tau and denote the longest relaxation time and the mean square end-to-end distance, respectively.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp

    Relaxation of a Single Knotted Ring Polymer

    Full text link
    The relaxation of a single knotted ring polymer is studied by Brownian dynamics simulations. The relaxation rate lambda_q for the wave number q is estimated by the least square fit of the equilibrium time-displaced correlation function to a double exponential decay at long times. The relaxation rate distribution of a single ring polymer with the trefoil knot appears to behave as lambda_q=A(1/N^)x for q=1 and lambda_q=A'(q/N)^x' for q=2 and 3, where x=2.61, x'=2.02 and A>A'. The wave number q of the slowest relaxation rate for each N is given by q=2 for small values of N, while it is given by q=1 for large values of N. This crossover corresponds to the change of the structure of the ring polymer caused by the localization of the knotted part to a part of the ring polymer.Comment: 13 pages, 5 figures, uses jpsj2.cl

    Nkx3.2 Promotes Primary Chondrogenic Differentiation by Upregulating Col2a1 Transcription

    Get PDF
    Background: The Nkx3.2 transcription factor promotes chondrogenesis by forming a positive regulatory loop with a crucial chondrogenic transcription factor, Sox9. Previous studies have indicated that factors other than Sox9 may promote chondrogenesis directly, but these factors have not been identified. Here, we test the hypothesis that Nkx3.2 promotes chondrogenesis directly by Sox9-independent mechanisms and indirectly by previously characterized Sox9-dependent mechanisms. Methodology/Principal Findings: C3H10T1/2 pluripotent mesenchymal cells were cultured with bone morphogenetic protein 2 (BMP2) to induce endochondral ossification. Overexpression of wild-type Nkx3.2 (WT-Nkx3.2) upregulated glycosaminoglycan (GAG) production and expression of type II collagen a1 (Col2a1) mRNA, and these effects were evident before WT-Nkx3.2-mediated upregulation of Sox9. RNAi-mediated inhibition of Nkx3.2 abolished GAG production and expression of Col2a1 mRNA. Dual luciferase reporter assays revealed that WT-Nkx3.2 upregulated Col2a1 enhancer activity in a dose-dependent manner in C3H10T1/2 cells and also in N1511 chondrocytes. In addition, WT-Nkx3.2 partially restored downregulation of GAG production, Col2 protein expression, and Col2a1 mRNA expression induced by Sox9 RNAi. ChIP assays revealed that Nkx3.2 bound to the Col2a1 enhancer element. Conclusions/Significance: Nkx3.2 promoted primary chondrogenesis by two mechanisms: Direct and Sox9-independen

    Largeā€scale calculations of excitation energies in coupled cluster theory : The singlet excited states of benzene

    Get PDF
    Algorithms for calculating singlet excitation energies in the coupled cluster singles and doubles (CCSD) model are discussed and an implementation of an atomicā€integral direct algorithm is presented. Each excitation energy is calculated at a cost comparable to that of the CCSD groundā€state energy. Singlet excitation energies are calculated for benzene using up to 432 basis functions. Basisā€set effects of the order of 0.2 eV are observed when the basis is increased from augmented polarized valence doubleā€zeta (augā€ccā€pVDZ) to augmented polarized valence tripleā€zeta (augā€ccā€pVTZ) quality. The correlation problem is examined by performing calculations in the hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3, as well as by using the CCSDR(3) perturbative triples corrections. The effect of triple excitations are less than 0.2 eV for all excitations except for the 2ā€‰1E2g state. The calculated excitation energies are compared with experiment and other theoretical [email protected]
    • ā€¦
    corecore