Introduction

QXMD is a Quantum Molecular Dynamics (QMD) simulation software with various eXtensions. QMD follows the trajectories of all atoms while computing interatomic forces quantum mechanically in the framework of density functional theory (DFT). [1] The QXMD software has been developed by Fuyuki Shimojo since 1994. [2] Since 1999, various extensions have been developed in collaboration with Rajiv Kalia, Aiichiro Nakano and Priya Vashishta. [3] The basic QXMD code is based on a plane-wave basis to represent electronic wave functions and pseudopotential (PP) methods to describe electron-ion interaction. Supported PPs include norm-conserving PP [4] and ultrasoft PP [5] . Electron-electron interaction beyond the mean-field Hartree approximation is included using various exchange-correlation functionals, with and without spin polarization: generalized gradient approximation (GGA) [6], DFT+U method for transition metals [7], van der Waals (vDW) functional for molecular crystals and layered materials [8], nonlocal correlation functional [9], and range-separated exact-exchange functional [10] [RN99]. Various unique capabilities included in the QXMD code (some of which are described in [11]) include:

1. Linear-scaling DFT algorithms [11] [12] [13]
2. Scalable algorithms on massively parallel computers [14] [15]
3. Nonadiabatic quantum molecular dynamics (NAQMD) to describe excitation dynamics [3]
4. Omni-directional multiscale shock technique (OD-MSST) to study shock response of materials [16] [17]

[1]	P. Hohenberg and W. Kohn. Inhomogeneous electron gas. Physical Review, 136(3B):B864–B871, 1964. URL: https://link.aps.org/doi/10.1103/PhysRev.136.B864, doi:10.1103/PhysRev.136.B864.

[2]	F. Shimojo, Y. Zempo, K. Hoshino, and M. Watabe. First-principles molecular-dynamics simulation of expanded liquid rubidium. Physical Review B, 52(13):9320–9329, 1995. URL: <Go to ISI>://A1995RY42500042, doi:10.1103/PhysRevB.52.9320.

[3]

(1, 2) Fuyuki Shimojo, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta. Linear-scaling density-functional-theory calculations of electronic structure based on real-space grids: design, analysis, and scalability test of parallel algorithms. Computer Physics Communications, 140(3):303–314, 2001. doi:10.1016/S0010-4655(01)00247-8.

[4]	N. Troullier and José Luriaas Martins. Efficient pseudopotentials for plane-wave calculations. Physical Review B, 43(3):1993–2006, 1991. URL: https://link.aps.org/doi/10.1103/PhysRevB.43.1993, doi:10.1103/PhysRevB.43.1993.

[5]	David Vanderbilt. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Physical Review B, 41(11):7892–7895, 1990. URL: https://link.aps.org/doi/10.1103/PhysRevB.41.7892, doi:10.1103/PhysRevB.41.7892.

[6]	John P. Perdew, Kieron Burke, and Matthias Ernzerhof. Generalized gradient approximation made simple. Physical Review Letters, 77(18):3865–3868, 1996. URL: https://link.aps.org/doi/10.1103/PhysRevLett.77.3865, doi:10.1103/PhysRevLett.77.3865.

[7]	A. I. Liechtenstein, V. I. Anisimov, and J. Zaanen. Density-functional theory and strong interactions: orbital ordering in mott-hubbard insulators. Physical Review B, 52(8):R5467–R5470, 1995. URL: https://link.aps.org/doi/10.1103/PhysRevB.52.R5467, doi:10.1103/PhysRevB.52.R5467.

[8]	Stefan Grimme. Semiempirical gga-type density functional constructed with a long-range dispersion correction. Journal of Computational Chemistry, 27(15):1787–1799, 2006. URL: http://doi.wiley.com/10.1002/jcc.20495, doi:10.1002/jcc.20495.

[9]	M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist. Van der waals density functional for general geometries. Physical Review Letters, 92(24):22–25, 2004. doi:10.1103/PhysRevLett.92.246401.

[10]	Jochen Heyd and Gustavo E. Scuseria. Efficient hybrid density functional calculations in solids: assessment of the heyd–scuseria–ernzerhof screened coulomb hybrid functional. The Journal of Chemical Physics, 121(3):1187–1192, 2004. URL: https://doi.org/10.1063/1.1760074, doi:10.1063/1.1760074.

[11]

(1, 2) Fuyuki Shimojo, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta. Divide-and-conquer density functional theory on hierarchical real-space grids: parallel implementation and applications. Physical Review B - Condensed Matter and Materials Physics, 77(8):1–12, 2008. doi:10.1103/PhysRevB.77.085103.

[12]

Fuyuki Shimojo, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta. Embedded divide-and-conquer algorithm on hierarchical real-space grids: parallel molecular dynamics simulation based on linear-scaling density functional theory. Computer Physics Communications, 167(3):151–164, 2005. doi:10.1016/j.cpc.2005.01.005.

[13]	E. Hernández, M. Gillan, and C. Goringe. Linear-scaling density-functional-theory technique: the density-matrix approach. Physical Review B - Condensed Matter and Materials Physics, 53(11):7147–7157, 1996. doi:10.1103/PhysRevB.53.7147.

[14]

Manaschai Kunaseth, Rajiv K. Kalia, Aiichiro Nakano, Ken-ichi Nomura, and Priya Vashishta. A scalable parallel algorithm for dynamic range-limited <i>n</i> -tuple computation in many-body molecular dynamics simulation. Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis on - SC ‘13, pages 1–12, 2013. URL: http://dl.acm.org/citation.cfm?doid=2503210.2503235, doi:10.1145/2503210.2503235.

[15]

Ken-Ichi Nomura, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta, Kohei Shimamura, Fuyuki Shimojo, Manaschai Kunaseth, Paul C. Messina, and Nichols A. Romerod. Metascalable quantum molecular dynamics simulations of hydrogen-on-demand. SC14: International Conference for High Performance Computing, Networking, Storage and Analysis, pages 661–673, 2014. URL: http://ieeexplore.ieee.org/document/7013041/, doi:10.1109/SC.2014.59.

[16]

Kohei Shimamura, Masaaki Misawa, Satoshi Ohmura, Fuyuki Shimojo, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta. Crystalline anisotropy of shock-induced phenomena: omni-directional multiscale shock technique. Applied Physics Letters, 108(7):071901–071901, 2016. URL: http://dx.doi.org/10.1063/1.4942191 http://aip.scitation.org/doi/10.1063/1.4942191, doi:10.1063/1.4942191.

[17]

Kohei Shimamura, Masaaki Misawa, Ying Li, Rajiv K. Kalia, Aiichiro Nakano, Fuyuki Shimojo, and Priya Vashishta. A crossover in anisotropic nanomechanochemistry of van der waals crystals. Applied Physics Letters, 107(23):231903–231903, 2015. URL: http://dx.doi.org/10.1063/1.4937268,http://aip.scitation.org/doi/10.1063/1.4937268, doi:10.1063/1.4937268.