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Adiabatic Processes for an Ideal Gas01:18

Adiabatic Processes for an Ideal Gas

When an ideal gas is compressed adiabatically, that is, without adding heat, work is done on it, and its temperature increases. In an adiabatic expansion, the gas does work, and its temperature drops. Adiabatic compressions actually occur in the cylinders of a car, where the compressions of the gas-air mixture take place so quickly that there is no time for the mixture to exchange heat with its environment. Nevertheless, because work is done on the mixture during the compression, its...
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Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package
06:37

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Published on: September 17, 2021

Ab initio non-adiabatic molecular dynamics.

Enrico Tapavicza1, Gregory D Bellchambers, Jordan C Vincent

  • 1Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, California 92697-2025, USA. filipp.furche@uci.edu.

Physical Chemistry Chemical Physics : PCCP
|September 27, 2013
PubMed
Summary
This summary is machine-generated.

Non-adiabatic molecular dynamics (NAMD) accurately models chemical reactions where the Born-Oppenheimer approximation fails. Recent advances in quantum-classical dynamics and time-dependent density functional theory (TDDFT) enable efficient ab initio NAMD simulations.

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Area of Science:

  • Computational Chemistry
  • Quantum Dynamics
  • Theoretical Chemistry

Background:

  • Adiabatic potential energy surfaces (PESs) based on the Born-Oppenheimer (BO) approximation are central to chemical reactivity theory.
  • The BO approximation fails for excited-state phenomena like radiationless decay and photochemical reactions due to strong couplings between BO PESs.
  • Non-adiabatic molecular dynamics (NAMD) is essential for simulating these processes.

Purpose of the Study:

  • To review recent advancements in ab initio NAMD simulations.
  • To highlight the impact of quantum-classical dynamics, analytical derivative methods, and time-dependent density functional theory (TDDFT) on expanding NAMD capabilities.
  • To showcase the application of surface-hopping TDDFT for photochemical reactions.

Main Methods:

  • Focus on atom-centered Gaussian basis sets for efficient ab initio NAMD simulations, particularly with hybrid density functionals.
  • Utilize analytical derivative techniques for high-precision calculation of forces and derivative couplings, crucial for stable dynamics.
  • Employ surface-hopping TDDFT to model photochemical reactions of excited states.

Main Results:

  • Demonstrated the performance of surface-hopping TDDFT for photochemical reactions in cyclohexadiene, vitamin D derivatives, and bicyclic cyclobutene.
  • Calculated quantum yields and excited state lifetimes show qualitative agreement with experimental data.
  • Achieved 0.2-0.4 ns total simulation time for systems with ~50 atoms using hybrid functionals and polarized double zeta valence basis sets on medium compute clusters.

Conclusions:

  • Recent developments significantly enhance the scope and efficiency of ab initio NAMD simulations.
  • Surface-hopping TDDFT provides a reliable method for studying excited-state photochemical processes.
  • Further research is needed to address open challenges and explore future directions in NAMD.