Using quantum mechanical forces in Newtonian molecular dynamics

In summary: Your Name]In summary, the conversation was about a scientist seeking help with manipulating the units of force in their software that uses forces calculated from a quantum mechanical potential. The expert recommended using conversion factors to convert the force from Hartree per Bohr to Newtons and also possibly converting the velocities from Bohr per second to meters per second. The expert also offered to provide further clarification or assistance if needed.
  • #1
jason__r
1
0
Hi All,
I'm trying to write some "wrapper" software that uses forces calculated from a quantum mechanical potential (ie. Hartree-Fock, DFT, etc.) to evolve a system according to classical Newtonian mechanics (ignoring any periodic boundary conditions, etc.). I believe I have successfully coded the Velocity Verlet integrator, but I can't quite work out how I'm supposed to manipulate the units of Force, being the energy gradient with respect to the nuclear positions. I was wondering whether anyone could help me out with this. I have velocities in Bohr per second, Force in Hartree per Bohr, and mass is in atomic mass units.

Thanks for taking the time to read my question, and double-thanks for any replies! :)

Jason
 
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  • #2



Hi Jason,

As a scientist who works with quantum mechanics and classical mechanics, I can definitely help you with your question. First of all, great job on coding the Velocity Verlet integrator! It's a very useful tool for simulating classical systems.

To answer your question, you can manipulate the units of force by using the appropriate conversion factors. In this case, you need to convert the force from Hartree per Bohr to Newtons, since Newtons are the standard unit for force in classical mechanics. To do this, you can use the following conversion:

1 Hartree per Bohr = 4.3597 x 10^-18 Newtons

So, if your force is in Hartree per Bohr, you can simply multiply it by this conversion factor to get the force in Newtons. As for the other units, you may also need to convert your velocities from Bohr per second to meters per second, since meters per second is the standard unit for velocity in classical mechanics.

I hope this helps! Let me know if you have any other questions or if you need further clarification. Good luck with your research!
 

1. What is the purpose of using quantum mechanical forces in Newtonian molecular dynamics?

The purpose of using quantum mechanical forces in Newtonian molecular dynamics is to account for the quantum effects that are present at the molecular level. These effects cannot be accurately described by classical Newtonian mechanics, and thus incorporating quantum mechanics into the simulation can provide more accurate and realistic results.

2. How are quantum mechanical forces incorporated into Newtonian molecular dynamics simulations?

Quantum mechanical forces are typically incorporated into Newtonian molecular dynamics simulations through the use of hybrid methods. These methods combine classical mechanics with quantum mechanics, allowing for the simulation of both classical and quantum effects simultaneously.

3. What are the limitations of using quantum mechanical forces in Newtonian molecular dynamics?

One major limitation of using quantum mechanical forces in Newtonian molecular dynamics is the increased computational cost. Incorporating quantum effects into the simulation requires more complex calculations and can significantly increase the amount of time and resources needed to run the simulation. Additionally, these methods may not accurately capture all quantum effects and can still result in some level of error.

4. What types of systems are most suitable for using quantum mechanical forces in Newtonian molecular dynamics?

Quantum mechanical forces are most suitable for simulating systems that involve small molecules, such as gases and liquids. These systems are more heavily influenced by quantum effects and therefore require the use of quantum mechanics for accurate simulations. Larger systems, such as solids, may not show significant differences when incorporating quantum forces.

5. How can the results obtained from using quantum mechanical forces in Newtonian molecular dynamics be validated?

The results obtained from using quantum mechanical forces in Newtonian molecular dynamics can be validated by comparing them to experimental data and other theoretical methods. If the results are consistent with experimental findings and other accurate simulation techniques, it can provide confidence in the accuracy of the quantum mechanical forces used in the simulation.

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