Gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach. II. Density functional and coupled cluster theory

2007 ◽  
Vol 126 (15) ◽  
pp. 154111 ◽  
Author(s):  
Andrea Ligabue ◽  
Stephan P. A. Sauer ◽  
Paolo Lazzeretti
Keyword(s):  
Current Density ◽  
Density Functional ◽  
Coupled Cluster ◽  
Magnetic Shielding ◽  
Continuous Transformation ◽  
Coupled Cluster Theory ◽  
Cluster Theory ◽  
Gauge Invariant ◽  
Shielding Constants ◽  
Nuclear Magnetic

scholarly journals A comparative study using state-of-the-art electronic structure theories on solid hydrogen phases under high pressures

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Ke Liao ◽  
Xin-Zheng Li ◽  
Ali Alavi ◽  
Andreas Grüneis
Keyword(s):  
Monte Carlo ◽  
Density Functional ◽  
High Pressures ◽  
State Of The Art ◽  
Solid Hydrogen ◽  
Coupled Cluster ◽  
Temperature Phase ◽  
Diffusion Monte Carlo ◽  
Coupled Cluster Theory ◽  
Cluster Theory

AbstractIdentifying the atomic structure and properties of solid hydrogen under high pressures is a long-standing problem of high-pressure physics with far-reaching significance in planetary and materials science. Determining the pressure-temperature phase diagram of hydrogen is challenging for experiment and theory due to the extreme conditions and the required accuracy in the quantum mechanical treatment of the constituent electrons and nuclei, respectively. Here, we demonstrate explicitly that coupled cluster theory can serve as a computationally efficient theoretical tool to predict solid hydrogen phases with high accuracy. We present a first principles study of solid hydrogen phases at pressures ranging from 100 to 450 GPa. The computed static lattice enthalpies are compared to state-of-the-art diffusion Monte Carlo results and density functional theory calculations. Our coupled cluster theory results for the most stable phases including C2/c-24 and P2$${}_{1}$$1/c-24 are in good agreement with those obtained using diffusion Monte Carlo, with the exception of Cmca-4, which is predicted to be significantly less stable. We discuss the scope of the employed methods and how they can contribute as efficient and complementary theoretical tools to solve the long-standing puzzle of understanding solid hydrogen phases at high pressures.

scholarly journals Spatial Contributions to 1H NMR Chemical Shifts of Free-Base Porphyrinoids

Chemistry ◽  
2021 ◽  
Vol 3 (3) ◽  
pp. 1005-1021
Author(s):  
Heike Fliegl ◽  
Maria Dimitrova ◽  
Raphael J. F. Berger ◽  
Dage Sundholm
Keyword(s):  
Current Density ◽  
Visual Inspection ◽  
Ring Current ◽  
Chemical Shifts ◽  
Magnetic Shielding ◽  
Free Base ◽  
Nmr Chemical Shifts ◽  
1H Nuclear Magnetic Resonance ◽  
Shielding Constants ◽  
Nuclear Magnetic

A recently developed methodology for calculating, analyzing, and visualizing nuclear magnetic shielding densities is used for studying spatial contributions including ring-current contributions to 1H nuclear magnetic resonance (NMR) chemical shifts of aromatic and anti-aromatic free-base porphyrinoids. Our approach allows a visual inspection of the spatial origin of the positive (shielding) and negative (deshielding) contributions to the nuclear magnetic shielding constants. Diatropic and paratropic current-density fluxes yield both shielding and deshielding contributions implying that not merely the tropicity of the current density determines whether the contribution has a shielding or deshielding character. Instead the shielding or deshielding contribution is determined by the direction of the current-density flux with respect to the studied nucleus.

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