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QuantumATK => General Questions and Answers => Topic started by: GJK on February 23, 2014, 16:50

Title: optimization-reg
Post by: GJK on February 23, 2014, 16:50

Hi,

Kindly explain me what is the difference between MD optimization and optimize geometry.When to use MD and when to use optimize geometry.Kindly explain about the parameters also.

One more question in the section optimize geometry we have Poisson solver with Multigrid FF2D and FFT.
Kindly tell me which option to prefer and why ,if we use
a) Molecular Configuration
b)Bulk Configuration
c) Device Configuration

Thanks in advance

Title: Re: optimization-reg
Post by: GJK on February 26, 2014, 04:08

Quote from: GJK on February 23, 2014, 16:50

Hi,

Kindly explain me what is the difference between MD optimization and optimize geometry.When to use MD and when to use optimize geometry.Kindly explain about the parameters also.

One more question in the section optimize geometry we have Poisson solver with Multigrid FF2D and FFT.
Kindly tell me which option to prefer and why ,if we use
a) Molecular Configuration
b)Bulk Configuration
c) Device Configuration

Thanks in advance

Title: Re: optimization-reg
Post by: GJK on February 27, 2014, 03:15

Hi,

I am waiting eagerly to get your suggestions.Kindly help me.


Regards
Janani.K

Title: Re: optimization-reg
Post by: Umberto Martinez on February 27, 2014, 09:05

Very very shortly, in a MD you simulate the motion of the atoms in time at a finite temperature.
In a geometry optimization you will use the forces to minimize the total energy of your configuration and find the equilibrium geometry.
Please, take a look to any solid state book.

About the parameters, you can find all the available parameters for the two methods here:
http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.optimizegeometry.html (http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.optimizegeometry.html)
http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.moleculardynamics.html (http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.moleculardynamics.html)


About the Poisson solver the short answer is:
device: use FFT2D unless you have spatial regions, then Multigrid.
bulk: FFT unless it is charged. In that case you will need Multigrid
molecule: Multigrid, multipole

then there are some special cases that you may consider, see for example the slab calculations in this tutorial: Tuning the work function of silver by deposition of ultrathin oxide layers (http://quantumwise.com/publications/tutorials/mini-tutorials/244#h6-setting-the-parameters-for-the-work-function-calculation)

Title: Re: optimization-reg
Post by: GJK on March 2, 2014, 17:11

Thank you Mr.Martinez