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An integral grid-based variational method applied to vibrational spectroscopy
Maurício Gustavo Rodrigues
Instituto Federal Catarinense (IFC)
Now you could share with me your questions, observations and congratulations
Create a topicWavefuntion and vibrational energies are generated in a simple way
Vibrational energies and spectroscopical parameters generated are very close to literature results
A new method is presented
Régis Casimiro Leal
Parabéns pelo trabalho pessoal, muito legal! Abraço p/ todos vocês!
Carlos Eduardo Vieira de Moura
Olá, Maurício. Parabéns pelo trabalho. Não tenho muito conhecimento sobre esta área, então gostaria de saber como este método proposto se compara com outros métodos disponíveis na literatura, em termos de custo computacional e acurácia. Que tipo de sistemas mais complexos vocês pretendem explorar?
Obrigado!
Maurício Gustavo Rodrigues
Olá, Carlos, obrigado pela pergunta. O método é um pouco mais pesado que o do Le Roy, por exemplo, e as previsões são mais ou menos as mesmas. Mas veja: é um algoritmo novo, que foi aplicado a alguns sistemas e ainda será aplicado em outros. O escopo aqui é esse, entende? Hoje, o grupo está aplicando o método no método HFR e de correlação eletrônica, principalmente. Mas vejo com bons olhos aplicar na espectroscopia vibracional, uma vez que os cálculos freq do gaussian, por exemplo, gera espectros através de métodos da física clássica. Ou seja, ainda tem bastante água pra rolar embaixo dessa ponte.
Muito obrigado, Carlos, espero ter respondido sua questão.
Maurício Gustavo Rodrigues
Quem por acaso quiser, estou nessa sala a disposição para conversarmos hoje.
Maurício Gustavo Rodrigues
If you would like to talk with me today, I'm in this link.
Annika Bande
Hi Maurício,
nice to see a Quantum Monte Carlo work (and thanks for presenting in English). I did my PhD in the field. I have a number of questions:
1. What is the QMC method you use? Variational, Fixed node, path integral?
2. Now you have used a Morse potential. In a real molecule you would do the vibrational calculation based on the optimized geometry with the given method. Is the method you use allowing for a geometry optimization? I know some QMC do have gradients.
3. When you compare the resulting vibrational energies: what is your error bar?
Thanks and enjoy the conference.
Annika (Bande)
Maurício Gustavo Rodrigues
Hello Annika. Could we talk a little bit in a meet? I am with my daughter and write in English now is quite impossible. If you don't mind, I'm here, meet.google.com/zfq-qfyr-cgi
Maurício Gustavo Rodrigues
Of course, if you can't talk with me now, I answer you as soon as possible.
Maurício Gustavo Rodrigues
Hello again, Annika. It's a pleasure to talk with you, I have already read some of your articles. I am having some hardware issues right now, so your first question was in presentation but it is not audible. We use VQMC method. The variational princicle is almost the only imposition of the algorithm. 2. No, our method is, nowadays, only for calculation of ro-vibrational wavefunctions and energies. It means (if I understood your question) that we use some potential curve generated from another place. In this work, Morse Potential. But I do wish that we publish an article soon that we apply our method from MRCI, CC and/or composite vibrational curve. There are some people using something different in way that you told about, but it is not the scope of our attention right now. 3. I don't think I understood your question. Are you interested in the error from the experimental results? Or the error from our calculation instead? In the case of the first one, our errors are quite small, specially if you see the results on another calculations like that. People uses grid from 100 to 1000 point, we are using only 50 and the results are very close to the experimental ones. About the error of the method, well. I don't know, I confess. Once the variational principle is used, the method intend to be exact, if I'm not completely wrong. So, I don't think the error bar could be applied in this case. But I am definetly not sure about this. As soon as possible I refresh this third question.
Anyway, thank you so much for your questions, it is a pleasure talk with you. I have classes on thursday in your lecture, but I will watch it later for sure. Thank you again.
Annika Bande
Hi Maurício,
thanks for your reply. I had watched another video-poster but then stopped my work evening at like 10 pm, so I see your reply only now. A life meeting would have been much nicer.
About question 3 this was only that in QMC you tend to give your energies as 276.8(6), i.e. you give an error bar in parentheses (or you indicate your standard deviation otherwise), because the Monte Carlo always is subject to statistics over all the imaginary time steps you run it after equilibration.
Cheers, Annika
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Maurício Gustavo Rodrigues
Grande Regis, saudades de você! Grande abraço.