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11

Scripts, Tutorials and Applications / electron phonon coupling as function of fermi shift

« Last post by huang96 on December 2, 2025, 16:52 »

I have a question about electron-phonon coupling simulation in Quantum ATK.
I was following this guide https://docs.quantumatk.com/tutorials/mobility/mobility.html to set up a model to calculate the e-ph coupling rate of graphene.
Also referred to this https://spdocs.synopsys.com/dow_retrieve/qsc-x/seg/quantumatk/X-2025.06/manual/Types/ElectronPhononCoupling/ElectronPhononCoupling.html to know how the function works.

Here comes the problem, I think e-ph coupling rate is a function of graphene's fermi level.
However, I cannot tune it either in the interface window nor the python codes.
For example, in the codes, it is like below where no input parameters as 'fermi shift'

electron_phonon_coupling = ElectronPhononCoupling(
    configuration=optimized_configuration,
    hamiltonian_derivatives=hamiltonian_derivatives,
    dynamical_matrix=dynamical_matrix,
    kpoints_fractional=kpoints_fractional,
    qpoints_fractional=qpoints_fractional,
    electron_bands=All,
    energy_tolerance=0.01 * eV,
    initial_state_energy_range=[-0.4, 0.4] * eV,
)

I do find one 'fermi shift' in the definition of inverseLfieTime:

inverse_life_time = electron_phonon_coupling.inverseLifeTime(phonon_modes=All, electron_bands=All, temperature=300*Kelvin, fermi_shift=0.0*eV, integration_method=GaussianBroadening(), refinement=1)

But it cannot be plot properly.
So by any chance anyone can take a look to see how to get a simulation result of e-ph coupling rate as function of fermi shift ?
Thanks in advance.

12

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by filipr on November 28, 2025, 11:18 »

We have recently been made aware that Nvidia has implemented algorithms that can do linear algebra operations using emulated floating point operations on tensor cores on GPUs that do not necessarily have many native FP64 units such as RTX 6000: https://developer.nvidia.com/blog/unlocking-tensor-core-performance-with-floating-point-emulation-in-cublas/

This requires using the newest CUDA version (and probably also newest drivers). We have not had time to do any experiments with this, but feel free to try yourself. Note that QuantumATK ships with CUDA 12.2, so you will have to modify the launcher script (bin/atkpython is just a Bash script that sets LD_LIBRARY_PATH and other relevant environment variables) so that the program picks up the right CUDA libraries.

13

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by filipr on November 26, 2025, 14:12 »

As noted above, the reason for this is that RTX cards do not have many FP64 units per streaming multiprocessor. From this table you can see that RTX 6000 has a single precision operation throughput of 91 TeraFLOPS, but only 1.4 TeraFLOPS for double precision, i.e. a fraction of 1/64 as I also explained earlier.

Besides that, GPUs are only good for tasks that can be heavily parallelized and not all algorithms scale equally well. On top of that transferring data from host RAM to GPU memory is very slow, especially on consumer cards, so one needs to go to quite large systems before the compute speedup compensates for the overhead of copying data to the GPU.

These issues are inherent to scientific computing, not just QuantumATK and are not really "fixable". If you want a worthwhile GPU speedup you need to get your hands on the GPUs designed for scientific workloads.

14

General Questions and Answers / Re: Issue on running MTP training simulation

« Last post by Lim changmin on November 26, 2025, 12:03 »

Thank you for the advice. I'll try it.

15

General Questions and Answers / Re: Issue on running MTP training simulation

« Last post by AsifShah on November 26, 2025, 04:36 »

Hi,

Just a small suggestion. Instead of going with MTP, I would suggest fine-tuning a MACE mode which is more accurate than MTP. The fine tuning is also very simple. You can go throught his tutorial.

 "https://docs.quantumatk.com/tutorials/mace-training-c-am-TiSi/mace-training-c-am-TiSi.html"

16

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by AsifShah on November 26, 2025, 04:34 »

On the same note,

I am using RTX 6000 Ada but there is no speedup. The CPU runs faster than GPU.
Any idea, why? Will these issues be resolved in next version of QATK?

17

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by dmicje12 on November 25, 2025, 08:17 »

Thanks you for your reply!

18

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by filipr on November 24, 2025, 14:01 »

I am not aware of any benchmarks on Volta series GPUs. We mainly have access to A-series hardware. Depending on the calculations you do the bottleneck of the program will often be in CUDAx libraries like cuBLAS and cuSolver, so you can search for benchmarks of these.

19

General Questions and Answers / Re: Questions Regarding GPU Acceleration

« Last post by dmicje12 on November 21, 2025, 03:01 »

Thank you for your response!
I would like to know how your team evaluated the acceleration performance of the V100. Was the improvement significant?
I understand that the V100 is certainly not as powerful as the A100 or H100, but how does the V100 compare to a server-grade CPU (such as the EPYC 7F72 shown in the manual)?
Thanks!

20

General Questions and Answers / Difference Between electrode_extension_lengths and equivalent_electrode_lengths

« Last post by kaihuang on November 21, 2025, 00:06 »

Hi all,

Could anyone clarify the physical meaning of electrode_extension_lengths in the device configuration, and how it influences the calculation results? The manual only states that it is “the desired equivalent electrode extension length of each electrode,” which is not very informative.

In a related forum discussion (https://forum.quantumatk.com/index.php?topic=10735.0), it was mentioned that the calculation results depend on this parameter. What is the underlying theory for this dependence?

We already have the parameter equivalent_electrode_lengths, which defines how much of the central region should be equivalent to the electrodes which is clear. But how is electrode_extension_lengths fundamentally different?

In older versions of the manual and ATK (e.g., https://docs.quantumatk.com/tutorials/atk_transport_calculations/atk_transport_calculations.html), this parameter did not exist.