Yes, when anharmonicity get stronger, the perturbative approach of d3q eventually breaks down. It is always possible to use stochastic (sscha) or molecular dynamics methods. Each method has trade-offs, in terms of: computational cost, ability to cope with strong anharmonicity, treatment of quantum ions/very low temperatures, and last but not least in my opinion, giving an insight to the physical processes.
regards Dr. Lorenzo Paulatto IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université phone: +33 (0)1 442 79822 / skype: paulatz http://www.impmc.upmc.fr/~paulatto/ (https://link.getmailspring.com/link/[email protected]/0?redirect=http%3A%2F%2Fwww.impmc.upmc.fr%2F~paulatto%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D) - https://anharmonic.github.io/ (https://link.getmailspring.com/link/[email protected]/1?redirect=https%3A%2F%2Fanharmonic.github.io%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D) 23-24/423 B115, 4 place Jussieu 75252 Paris CX 05 On Mar 31 2021, at 4:35 am, Terry Frankcombe <[email protected]> wrote: > While we are talking about interesting ways to include anharmonic > effects, it's worth taking a look at SSCHA: http://sscha.eu/ > > Not necessarily computationally inexpensive. > > On Wed, 2021-03-31 at 07:20 +0900, Kazume NISHIDATE wrote: > > > 2021/03/31 1:00、Lorenzo Paulatto <[email protected]>のメール: > > > > > > Hello you can take into account anharmonicity with the d3q code which is > > > included in QE, > > > > > > This may be the most sophisticated way to account for the > > anharmonicity from first principle. I'm impress by the ingeniousness. > > Thank you for your notice. > > > > btw- > > The methods described in my previous message are heavily relying upon > > a brute force manner. The only advantage of the method should be the > > automatic inclusion of higher order terms beyond the third-order, but > > of course its resolution, especially when it was obtained by MD, would > > be very low. > > > > > > > > > > best regards > > kazume NISHIDATE > > 敬具 西館数芽 > > > > [email protected] > > [email protected] > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > > users mailing list [email protected] > > https://lists.quantum-espresso.org/mailman/listinfo/users > > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users >
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