Size-consistent multireference configuration interaction method through the dressing of the norm of determinants

A new determinant-specific, effective change (‘dressing’) of the norm of the multireference configuration interaction (MRCI) wavefunction is proposed in order to achieve the size-consistency of the MRCI method. The new approach provides a unifying framework for analysis of size-consistent extensions of the MRCI method that are based on the coupled pair functional (CPF) strategy and lead to simplified computations of the analytical gradients. Using the new framework, a generalized multireference full coupled pair functional (MR-FCPF) method is introduced. The MR-FCPF method may be viewed as a functional counterpart of the recently proposed generalized (‘full’) coupled electron pair approximation (CEPA), referred to as the size-consistent self-consistent CI ((SC)²CI) method. A straightforward extension of the MR-FCPF method leads to a pseudo-functional form of the coupled cluster (CC) type formalisms. Therefore, the new approach may be used to introduce a simple alternative to existing CC-type gradient techniques. The new procedure is formally derived and compared with similar methods from the literature. Model systems calculations (H₂O, LiF, CH⁺ ₂) are further used to demonstrate the effect of various approximations and to elucidate the hierarchy of functional MR-CEPA schemes.     

Theoretical and experimental study of quadrupolar echoes for half-integer spins in static solid-state NMR

Numerical simulations of powder spectra produced by a two-pulse sequence applied to a quadrupolar nuclei system of half-integer spin number make it possible to propose simple experimental instructions to record static echo spectra with minimum lineshape distortion. Calculations take into account quadrupolar (first and second orders), shielding, scalar and inhomogeneous dipolar interactions as well as the radiofrequency pulse specifications (strength, duration, phase). The suggested instructions have been checked experimentally in different cases: for a large spin number system with Li⁹³NbO₃, when two interactions are present with a ^63/65Cu complex, and in the two-site system of ⁸⁷Rb₂SO₄.     

Theoretical and experimental assessment of single- and multiple-quantum cross-polarization in solid state NMR

Continuous wave cross-polarization (CP) NMR experiments with magic angle spinning (MAS) are reviewed for the case of isolated spin pairs I-S, with spin quantum numbers I = ½ and S ½ (1/2, 3/2, …). For two spin-1/2 nuclei, the Hartmann-Hahn matching conditions are examined at various sample rotation rates ν_R, especially with regard to off-resonance behaviour. In addition to signal enhancement, the CPMAS experiment can be used for the selective determination of inter-nuclear distances between spin-1/2 nuclei. Theoretical examination of the CP transfers to single-quantum (1Q-CPMAS) and multiple-quantum (MQ-CPMAS) levels of quadrupolar nuclei is presented. Simple analytical formulae describing the Hartmann-Hahn matching under various experimental conditions are verified using computer simulations of the spin density matrix under MAS, and the experimental data. The strategies for the most efficient acquisition of 1Q-CPMAS and MQ-CPMAS spectra are extensively discussed.     

Molecular dynamics of polymers with explicit but frozen hydrogens

A new form of holonomic constraint, called a conic constraint, is introduced for the purpose of eliminating the fast vibrations of hydrogen atoms in molecular simulations of systems of aliphatic chains. It can easily be combined with bond constraints in SHAKE/RATTLE algorithms for which a unified tolerance criterion is defined. The new form of constraint allows the use of rather large time steps (in the 2–3 fs range). The procedure is illustrated for a full atomic model of polypropylene.     

组合脉冲宽带激发2H-平均哈密顿理论计算研究

四级核回波实验通常需要射频脉冲能够激发谱宽超过100 kHz 的信号．在最近的研究中,作者发现组合脉冲COM-II (9018090135 45) 能够在氘核的四级核回波实验中实现宽带激发．此外,作者还结合了八步相位循环的方法,有效消除了由有限脉宽效应造成的谱图扭曲现象．利用了平均哈密顿原理,对该方法进行了理论计算研究．作者采用了自旋为1 的矩阵算符,通过计算解释了八步相位循环能够消除谱图扭曲的原因．