[CP2K-user] [CP2K:13624] Some questions about using RT-TDDFT method in cp2k code to calculate spectrum

[xio...@gmail.com]

Dear Mario,



*Once again, I am grateful for your help. You have helped me a lot!*
*May you be happy, healthy and happy! *

Lin 
在2020年7月11日星期六 UTC+8 下午8:21:35<mar... at student.uva.nl> 写道：

> Dear Lin,
>
> https://manual.cp2k.org/trunk/CP2K_INPUT/MOTION/MD.html#TIMESTEP  
> Timestep section tells us:
>
> Default value: 5.00000000E-001
> Default unit: <https://manual.cp2k.org/trunk/units.html> [fs]
>
> So timestep is in fs. As for suggested values, I don't know. I didn't 
> manage. To get higher excitation energies you will need a smaller timestep, 
> otherwise these are "invisible" in the signal.
>
> Steps means how many timesteps are calculated (so 100 steps with 
> stepsize 1 would be 100 fs), more timesteps means less uncertainty in your 
> Fourier transform, giving more distinct peaks (I think).
>
> To figure out what the right timestep and steps are, you can take a look 
> at some literature and compare with experts that you get the same value. 
> And then also play around with stepsize and steps to see if your spectrum 
> changes a lot. The spectrum should be independent of stepsize if you are 
> around the right region. 
>
> Mario 
>
> On Sat, Jul 11, 2020 at 10:11 AM xio... at gmail.com <xio... at gmail.com> 
> wrote:
>
>>
>> Dear  Mario,
>>      
>> Thank you very much for your help. In fact, I have just started using 
>> cp2k software. I have a question before you reply to me, that is why there 
>> is no *dat file in my output files. But now I understand that I need to add 
>> the 'FILENAME output' keyword in the 'MOMENTS' subsection.
>>
>> Still, I have one question to ask you: What does the value of 'STEPS' in 
>> the 'MD' section of rt-TDDFT specifically mean? The interpretation of the 
>> official website is ambiguous. To calculate the spectra of different 
>> systems, do you have any suggestions for setting the STPES and TIMESTEP 
>> keywords?
>>
>> Best wishes,
>>
>> Lin
>> 在2020年7月11日星期六 UTC+8 上午2:29:44<mar... at student.uva.nl> 写道：
>>
>>> Dear Lin,
>>>
>>> I am not at all an expert on the issue, but I do have this example file 
>>> online. Also once you obtain the dipole moment as a function of time, you 
>>> can perform a Fourier transform of the data. I have attached a python 
>>> script to transform the data. Make sure it works properly yourself and make 
>>> sure you read about why this works :-). The output you want for the 
>>> spectrum should be called something like ch2o_pbe_rtp-output-moments.dat. I 
>>> tried this for quantum dots and it didn't work. Maybe different timestep 
>>> and basis/ potential are needed. Also, I don't know if the script can 
>>> handle these small numbers. 
>>>
>>> Good luck,
>>>
>>> Mario
>>>
>>>
>>>
>>> On Fri, Jul 10, 2020 at 4:03 PM lin xiong <xio... at gmail.com> wrote:
>>>
>>>> Hi all,
>>>>     
>>>>
>>>>     Recently I learned that cp2k code has two ways to calculate the 
>>>> absorption spectrum, namely real time propagation TDDFT and TDDFPT. I would 
>>>> like to ask some questions about using rt-TDDFT to calculate the spectra.
>>>>
>>>>     1. First of all, I would like to ask if my input file is correct? 
>>>> If the input file is correct, then there are two additional questions: 2. 
>>>> In which file (as shown in the figure below) is the data used to draw the 
>>>> spectrum stored? 3. How to use these data to plot the spectrum? 
>>>>
>>>> [image: 25.jpg]
>>>>
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