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Related Concept Videos

Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

268
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
268
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

632
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
632
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

959
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
959
Nuclear Overhauser Enhancement (NOE)01:07

Nuclear Overhauser Enhancement (NOE)

645
Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling.  This phenomenon, called the Nuclear Overhauser Enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring...
645

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Updated: Jun 11, 2025

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Very-Large-Scale GPU-Accelerated Nuclear Gradient of Time-Dependent Density Functional Theory with Tamm-Dancoff

Inkoo Kim1,2, Daun Jeong1, Leah P Weisburn2

  • 1Innovation Center, Samsung Electronics, Hwaseong 18448, Republic of Korea.

Journal of Chemical Theory and Computation
|October 7, 2024
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Summary

We developed a fast, multi-GPU method for calculating nuclear gradients in time-dependent density functional theory (TDDFT). This approach accelerates complex quantum chemistry simulations on modern high-performance computing systems.

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Area of Science:

  • Computational Chemistry
  • Quantum Mechanics
  • High-Performance Computing

Background:

  • Modern graphics processing units (GPUs) offer significant computational power.
  • Accurate calculation of molecular properties requires efficient theoretical methods.

Purpose of the Study:

  • To present a high-performance, multi-GPU implementation of analytical nuclear gradients for Kohn-Sham time-dependent density functional theory (TDDFT).
  • To demonstrate the algorithm's efficiency on large-scale systems.

Main Methods:

  • Implementation of multi-GPU algorithms for TDDFT nuclear gradients using the Tamm-Dancoff approximation (TDA) and Gaussian-type atomic orbitals.
  • Development of GPU-efficient algorithms for derivatives of electron repulsion integrals and exchange-correlation functionals.
  • Application to a large biomolecule (green fluorescent protein) with explicit solvent.

Main Results:

  • The TDA-TDDFT gradient calculation for a 4353-atom system was performed.
  • Favorable parallel efficiencies were achieved on 256 Nvidia A100 GPUs, with >70% efficiency up to 64 GPUs and 31% with 256 GPUs.

Conclusions:

  • The developed multi-GPU implementation effectively leverages high-performance computing resources.
  • This method significantly accelerates quantum chemistry calculations for large molecular systems.