kmc mobility and external field
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Tobias Koch
Feb 3, 2020, 6:21:18 AM2/3/20
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Hello,
We have got some remarks on the evaluation of the mobility in kmc_multiple and the projection of the velocity vector on the external field $\mathbf{F}^{\text{ext}}$.
We have got some remarks on the evaluation of the mobility in kmc_multiple and the projection of the velocity vector on the external field $\mathbf{F}^{\text{ext}}$.
Due to our knowledge the mobility should be determined as follows:
$$
\mu = \frac{ \langle \mathbf{v} \rangle \mathbf{U}^{\text{ext}} }{ | \mathbf{F}^{\text{ext}} | \cdot | \mathbf{F}^{\text{ext}}| }
= \frac{ \langle \mathbf{v} \rangle \mathbf{e}_{\mathbf{F}^{\text{ext}}} }{ | \mathbf{F}^{\text{ext}}| }
$$
In the kmcmultiple.h one finds:
// calculate mobilities
//double absolute_field = sqrt(_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ);
if (_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ != 0.0)
{
myvec average_mobility = myvec (0.0,0.0,0.0);
myvec fieldfactors = myvec (0.0, 0.0, 0.0);
if (_fieldX != 0)
{
fieldfactors.setX(1.0E4/_fieldX);
}
if (_fieldY != 0)
{
fieldfactors.setY(1.0E4/_fieldY);
}
if (_fieldZ != 0)
{
fieldfactors.setZ(1.0E4/_fieldZ);
}
cout << endl << "Mobilities (cm^2/Vs): " << endl;
for(unsigned int i=0; i<numberofcharges; i++)
{
myvec velocity = carrier[i]->dr_travelled/simtime;
myvec mobility = elementwiseproduct(velocity, fieldfactors);
average_mobility += mobility;
cout << std::scientific << " charge " << i+1 << ": ";
if (_fieldX != 0)
{
cout << std::scientific << "muX=" << mobility.getX() << " ";
}
if (_fieldY != 0)
{
cout << std::scientific << "muY=" << mobility.getY() << " ";
}
if (_fieldZ != 0)
{
cout << std::scientific << "muZ=" << mobility.getZ() << " ";
}
cout << endl;
}
The deviations / irritations only occure, if the external field vector is not aligned parallel to the simulation box vectors.
For a correct projection one should evaluate something like this:
// calculate mobilities
double absolute_field = sqrt(_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ);
if (_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ != 0.0)
{
myvec average_mobility = myvec (0.0,0.0,0.0);
myvec fieldfactors = myvec (0.0, 0.0, 0.0);
if (_fieldX != 0)
{
fieldfactors.setX((1.0E4*_fieldX)/absolute_field/absolute_field);
}
if (_fieldY != 0)
{
fieldfactors.setY((1.0E4*_fieldY)/absolute_field/absolute_field);
}
if (_fieldZ != 0)
{
fieldfactors.setZ((1.0E4*_fieldZ)/absolute_field/absolute_field);
}
cout << endl << "Mobilities (cm^2/Vs): " << endl;
for(unsigned int i=0; i<numberofcharges; i++)
{
myvec velocity = carrier[i]->dr_travelled/simtime;
myvec mobility = elementwiseproduct(velocity, fieldfactors);
average_mobility += mobility;
cout << std::scientific << " charge " << i+1 << ": ";
if (_fieldX != 0)
{
cout << std::scientific << "muX=" << mobility.getX() << " ";
}
if (_fieldY != 0)
{
cout << std::scientific << "muY=" << mobility.getY() << " ";
}
if (_fieldZ != 0)
{
cout << std::scientific << "muZ=" << mobility.getZ() << " ";
}
cout << endl;
}
Maybe someone can help us concerning this issue?
Best wishes Jim and Tobias.
$$
\mu = \frac{ \langle \mathbf{v} \rangle \mathbf{U}^{\text{ext}} }{ | \mathbf{F}^{\text{ext}} | \cdot | \mathbf{F}^{\text{ext}}| }
= \frac{ \langle \mathbf{v} \rangle \mathbf{e}_{\mathbf{F}^{\text{ext}}} }{ | \mathbf{F}^{\text{ext}}| }
$$
In the kmcmultiple.h one finds:
// calculate mobilities
//double absolute_field = sqrt(_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ);
if (_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ != 0.0)
{
myvec average_mobility = myvec (0.0,0.0,0.0);
myvec fieldfactors = myvec (0.0, 0.0, 0.0);
if (_fieldX != 0)
{
fieldfactors.setX(1.0E4/_fieldX);
}
if (_fieldY != 0)
{
fieldfactors.setY(1.0E4/_fieldY);
}
if (_fieldZ != 0)
{
fieldfactors.setZ(1.0E4/_fieldZ);
}
cout << endl << "Mobilities (cm^2/Vs): " << endl;
for(unsigned int i=0; i<numberofcharges; i++)
{
myvec velocity = carrier[i]->dr_travelled/simtime;
myvec mobility = elementwiseproduct(velocity, fieldfactors);
average_mobility += mobility;
cout << std::scientific << " charge " << i+1 << ": ";
if (_fieldX != 0)
{
cout << std::scientific << "muX=" << mobility.getX() << " ";
}
if (_fieldY != 0)
{
cout << std::scientific << "muY=" << mobility.getY() << " ";
}
if (_fieldZ != 0)
{
cout << std::scientific << "muZ=" << mobility.getZ() << " ";
}
cout << endl;
}
The deviations / irritations only occure, if the external field vector is not aligned parallel to the simulation box vectors.
For a correct projection one should evaluate something like this:
// calculate mobilities
double absolute_field = sqrt(_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ);
if (_fieldX*_fieldX + _fieldY*_fieldY + _fieldZ*_fieldZ != 0.0)
{
myvec average_mobility = myvec (0.0,0.0,0.0);
myvec fieldfactors = myvec (0.0, 0.0, 0.0);
if (_fieldX != 0)
{
fieldfactors.setX((1.0E4*_fieldX)/absolute_field/absolute_field);
}
if (_fieldY != 0)
{
fieldfactors.setY((1.0E4*_fieldY)/absolute_field/absolute_field);
}
if (_fieldZ != 0)
{
fieldfactors.setZ((1.0E4*_fieldZ)/absolute_field/absolute_field);
}
cout << endl << "Mobilities (cm^2/Vs): " << endl;
for(unsigned int i=0; i<numberofcharges; i++)
{
myvec velocity = carrier[i]->dr_travelled/simtime;
myvec mobility = elementwiseproduct(velocity, fieldfactors);
average_mobility += mobility;
cout << std::scientific << " charge " << i+1 << ": ";
if (_fieldX != 0)
{
cout << std::scientific << "muX=" << mobility.getX() << " ";
}
if (_fieldY != 0)
{
cout << std::scientific << "muY=" << mobility.getY() << " ";
}
if (_fieldZ != 0)
{
cout << std::scientific << "muZ=" << mobility.getZ() << " ";
}
cout << endl;
}
Maybe someone can help us concerning this issue?
Best wishes Jim and Tobias.
Denis Andrienko
Feb 3, 2020, 10:24:33 AM2/3/20
to votc...@googlegroups.com
Hi Tobias,
You are right, this will work only if the field is along x, y, or z, otherwise it is wrong. We are aware of it.
This 'fix' has been added by and external contributor and accepted by Christoph without much checking some time ago:
Are you interested in the full mobility tensor? It will not take much time to fix this if needed.
Also note that I have moved the ctp and csg developments of the Max Planck groups to a new repository,
We are in the process of restructuring the repo.
Best,
Denis
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Christoph Junghans
Feb 3, 2020, 1:46:13 PM2/3/20
to votc...@googlegroups.com
On Mon, Feb 3, 2020 at 8:24 AM 'Denis Andrienko' via votca-ctp <votc...@googlegroups.com> wrote:
Hi Tobias,You are right, this will work only if the field is along x, y, or z, otherwise it is wrong. We are aware of it.This 'fix' has been added by and external contributor and accepted by Christoph without much checking some time ago:
To view this discussion on the web visit https://groups.google.com/d/msgid/votca-ctp/CALe%3D2yXKet5tSViiJoSLZYaeO6Rw_ooFCKhyj9xDf4RpnnGbPA%40mail.gmail.com.
Tobias Koch
Feb 6, 2020, 10:03:24 AM2/6/20
to votca-ctp
The code from seems to exhibit the same error in the evaluation of the projection of <v> on F^ext.
Christoph Junghans
Feb 6, 2020, 10:08:15 AM2/6/20
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On Thu, Feb 6, 2020 at 8:03 AM Tobias Koch <tobiaskoc...@gmail.com> wrote:
>
> The code from razziel89 seems to exhibit the same error in the evaluation of the projection of <v> on F^ext.
Could you create a pull request for the correct projection you proposed?
>
> The code from razziel89 seems to exhibit the same error in the evaluation of the projection of <v> on F^ext.
Christoph
>>
>>
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Tobias Koch
Feb 10, 2020, 9:00:48 AM2/10/20
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Ok, we have tried to include our proposal.
Best wishes
Jim and Tobias
Am Donnerstag, 6. Februar 2020 16:08:15 UTC+1 schrieb Christoph Junghans:
On Thu, Feb 6, 2020 at 8:03 AM Tobias Koch <tobiaskoc...@gmail.com> wrote:
>
> The code from razziel89 seems to exhibit the same error in the evaluation of the projection of <v> on F^ext.
Could you create a pull request for the correct projection you proposed?
Christoph
>>
>>
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