MBXASPY is a python software package initiated by Yufeng Liang at the Molecular Foundry (TMF), Lawrence Berkeley National Laboratory (LBNL), for predicting x-ray spectra using the determinant formalism. The determinant formalism is based on the independent-electron approximation as used in the density-functional theory (DFT) and hence the many-body wavefunctions used in Fermi's Golden rule take a form of a single Slater determinant. The orbitals for constructing the initial/final-state Slater determinant are obtained from DFT calculations. The determinant approach for free-electron systems is equivalent to the MND theory.
To run MBXASPY, you need to first generate eigenvalues and eigenvectors of your Hamiltonian, either from DFT or from tight-binding models. At this stage, MBXASPY is seamingless interfaced with a Fortran software package, ShirleyXAS, that performs DFT and XAS calculations at a one-body level. ShirleyXAS is modified based on Quantum Espresso 4.3 by David Prendergast at TMF. There are two main advantages of running ShirleyXAS to feed the input for MBXASPY:
- ShirleyXAS employs ultrasoft pseudopotentials in PAW formalism, which is fast for large systems or systems with transition metals. A version of pseudopotential library can be found in here.
- ShirleyXAS carries out an efficient band structure extrapolation (developed by Eric L. Shirley) to improve quality of x-ray spectra, particularly the smoothness of the extended x-ray absorption fine structure.
If you would like to perform the determinant calculation without worrying too much about installation and supercomputing, please contact David's group at TMF for accessiblity to ShirleyXAS and more guidance. We have installed a module on our local computing cluster of LBNL. If you are a user of the cluster, you may simply load it by
module load MBXAS
The MBXAS contains some automatic scripts that carry out the ShirleyXAS + MBXASPY calculation in a convenient manner. You just need to get your structure ready and change a few parameters in the input file. Then you can just press and go ! A manual for how to use the MBXAS module can be found in the doc directory. A separate manual for MBXASPY can be found in here. Please generously cite the below references if you are using the MBXASPY code.
Currently, you may use MBXASPY to obtain x-ray absorption spectra (XAS) and x-ray photoemission spectra (XPS) at the level of the MND theory. One important application so far is to interpret the O K edge spectra for transition metal oxides. The authors are also actively looking for other applications that require the determinant method.
The develop branch can handle eigenvalues and eigenvectors from tight-binding models by setting scf_type ='model'. The RIXS branch for simulating resonant inelastic x-ray scattering (RIXS) and the emission branch for simulating x-ray emission spectra based on the determinant method are being developed and tested.
Please refer to the Chapter 2 of the Shirley + MBXASPY manual for several representative examples with detailed instructions. Sample input and output files can be found here.
- Interface MBXASPY with other popular DFT codes, such as higher versions of Quantum Espresso that use norm-conserving pseudopotentials, GPAW that is also based on python.
- Use HSE functionals in the DFT input.
- Continue to test the RIXS branch (no valence e-h interaction included ) against a wide class of materials.
- Combine the time-dependent density-functional theory (TDDFT) with the determinant formalism for XAS and RIXS.
- Yufeng Liang, John Vinson, Sri Pemmaraju, Walter S. Drisdell, Eric L. Shirley, and David Prendergast,
Accurate x-ray spectral predictions: an advanced self-consistent-field approach inspired by many-body perturbation theory, Phys. Rev. Lett. 118, 096402 (2017). - Yufeng Liang and David Prendergast, Quantum many-body effects in x-ray spectra efficiently computed using a basic graph algorithm, Phys. Rev. B 97, 205127 (2018).
- Yufeng Liang and David Prendergast, Taming convergence in the determinant approach for x-ray excitation spectra, Phys. Rev. B 100, 075121 (2019).
- Chang-Ming Jiang, Sebastian E. Reyes-Lillo, Yufeng Liang, Yi-Sheng Liu, et al, Electronic Structure and Performance Bottlenecks of CuFeO_2 Photocathodes, Chem. Mater. 31, 2524 (2019).
- Sebastian A. Howard, Christopher N. Singh, Galo J. Paez, Matthew J. Wahila, et al, Direct observation of delithiation as the origin of analog memristance in Li_xNbO_2, APL Materials 7, 071103 (2019)
- Matthew J. Wahila, Galo Paez, Christopher N. Singh, Anna Regoutz, et al, Evidence of a second-order Peierls-driven metal-insulator transition in crystalline NbO_2, Phys. Rev. Mater. 3, 074602 (2019)
- Galo J Paez, Christopher N Singh, Matthew J Wahila, Keith E Tirpak, et al, Simultaneous Structural and Electronic Transitions in Epitaxial VO_2/TiO_2 (001), Phys. Rev. Lett. 124, 196402 (2020)