Related Experiment Video
Updated: Jun 24, 2026
08:43
A Fluorescence Fluctuation Spectroscopy Assay of Protein-Protein Interactions at Cell-Cell Contacts
Published on: December 1, 2018
Rate constants calculation with a simple mixed quantum/classical implementation of the flux-flux correlation function
1Centro de Estudios e Investigaciones, Universidad Nacional de Quilmes, Saenz Pena 352, B1876BXD Bernal, Argentina. juliana@unq.edu.ar
The Journal of Chemical Physics
|April 2, 2009
Summary
A mixed quantum/classical method accurately calculates reaction rate constants for a model system. This approach shows promise for studying direct polyatomic gas-phase reactions.
Area of Science:
- Chemical Physics
- Quantum Mechanics
- Reaction Dynamics
Background:
- Evaluating reaction rate constants is crucial for understanding chemical processes.
- Accurate theoretical methods are needed for complex chemical reactions.
- The flux-flux correlation function method offers a pathway for rate constant calculations.
Purpose of the Study:
- To implement and test a mixed quantum/classical (mixed-Q/C) approach for calculating reaction rate constants.
- To assess the accuracy of the mixed-Q/C method for a two-dimensional model system.
- To explore the applicability of this method for direct polyatomic gas-phase reactions.
Main Methods:
- A mixed quantum/classical implementation of the flux-flux correlation function method was developed.
- A two-dimensional model system with an Eckart barrier (similar to H + H2) coupled to a harmonic oscillator was used.
- Rate constants were evaluated across a temperature range of 140–300 K.
Main Results:
- The mixed-Q/C method provided fairly accurate rate constants for the model system.
- Accuracy was maintained when the reaction system exhibited minimal recrossings.
- The study demonstrated the method's potential for more complex systems.
Conclusions:
- The developed mixed quantum/classical flux-flux correlation function method is a viable approach for calculating reaction rate constants.
- This methodology shows potential for extension to direct polyatomic reactions in the gas phase.
- The accuracy of the method is dependent on the degree of recrossing in the reaction system.
Related Concept Videos
01:25Calculation of Electric Flux
Consider the electric field of an oppositely charged, parallel-plate system and an imaginary box between those plates. Let the bottom face of the box be ABCD, and the top face be FGHK. The electric field between the plates is uniform and points from the positive plate toward the negative plate. The calculation of this field's flux through the box's various faces shows that the net flux through the box is zero. Why does the flux cancel out here?
01:24Calculation of First-Law Quantities II
The first law of thermodynamics establishes that the change in internal energy of a system is given by ΔU = q + w, where q is the heat exchanged, and w is the work performed. For a perfect gas, both internal energy (U) and enthalpy (H) depend solely on temperature. Consequently, for any change of state, whether reversible or irreversible, the internal energy change is determined by integrating the heat capacity at constant volume, and the enthalpy change by integrating the heat capacity at...
01:25Calculation of First Law Quantities I
Thermodynamic systems undergoing phase transitions or temperature changes experience energy transfer in the form of heat (q) and work (w). For a reversible phase change at constant temperature (T) and pressure (p), the process involves no chemical reaction but results in energy exchange between distinct phases.The heat transferred during this process corresponds to the latent heat of transition, which is the amount of heat energy absorbed or released by a substance when it changes from one...
01:12Classical Mechanics
Classical mechanics provides a mathematical description of the motion of bodies under the influence of forces. A key principle within this field is the work-energy theorem, which establishes a bridge between the net work done on an object and its kinetic energy.The work-energy theorem states that the net work done on a particle by all the forces acting on it equals the change in its kinetic energy.In simple terms, the work-energy theorem is a method to analyze the effects of forces on an...
01:26Reaction Mechanisms: The Steady-State Approximation
The steady-state approximation, also referred to as the quasi-steady-state approximation to differentiate it from a true steady state, is a widely used method for simplifying calculations in complex reaction mechanisms. This approach is particularly useful when dealing with multi-step reactions that involve reverse reactions or several steps, which can significantly increase mathematical complexity and make the reactions nearly unsolvable analytically.The steady-state approximation operates on...
02:39The Integrated Rate Law: The Dependence of Concentration on Time
While the differential rate law relates the rate and concentrations of reactants, a second form of rate law called the integrated rate law relates concentrations of reactants and time. Integrated rate laws can be used to determine the amount of reactant or product present after a period of time or to estimate the time required for a reaction to proceed to a certain extent. For example, an integrated rate law helps determine the length of time a radioactive material must be stored for its...