Dear Psi-K community,

I'm very proud to announce the first public release of a new code in the Quantum-ESPRESSO family. The D3Q code can compute the third derivative of the total energy with respect to three generic phonons. The code is much more efficient than any finite differences code, using the 2n+1 theorem on top of density functional perturbation theory (DFPT). The current release can treat:

• insulators, semiconductors and metals

• LDA and GGA functionals

• k-points

• norm conserving pseudopotentials

The third derivatives aren't of much use by themselves, that's why we bundle the D3Q code with the thermal2 suite of codes to compute intrinsic phonon-phonon interactions and solve the Boltzmann transport equation. This suite of codes can compute:

• phonon lifetime and linewidth from ph-ph interaction

• phonon self-energy from the Bubble (thid order) diagram

• final state decomposition of phonon decay process, over energy and q-points

• phonon spectral function

• thermal conductivity in the single mode approximation (SMA) of the linearized Boltzmann Transport Equation (BTE)

• thermal conductivity with exact solution of the BTE. This solution is computed using a variational form, minimized via a preconditioned conjugate gradient algorithm: guaranteed to converge, usually in less than 10 iterations

• inclusion of isotopic disorder and mass substitution defects

• effect of grain size and finite transverse dimension (e.g. nanotubes) using the Casimir formalism

• simultaneous calculation of many temperatures/smearings

• in addition to using our force constants from DFPT, we support importing 3-body force constants computed via finite differences with the thirdorder.py code (experimental!)

• parallel computing implemented with MPI (with great scalability up to thousand of CPUs) and OpenMP (optimal for memory reduction)

You can download the code (to be compiled together with QE 5.4.0) including extensive examples, tutorials and manuals from the project website on the qe-forge: http://www.qe-forge.org/gf/project/d3q/

We have also set up a specific mailing list for users help requests, available at: http://www.qe-forge.org/mailman/listinfo/d3q-users

The main code authors for the D3Q and thermal2 codes are Lorenzo Paulatto, Michele Lazzeri, Giorgia Fugallo, Andrea Cepellotti, Tobias Wassmann, Francesco Mauri. Contributions, in the form of code, testing or insight, have also come from Nicola Marzari, Ion Errea, Raffaello Bianco, Maksim Markov, Nathalie Vast, Davide Campi, Guilherme Ribeiro. The original d3.x code, on which the current one is based, was also written by Stefano de Gironcoli.

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