ABACUS (Atomic-orbtial Based Ab-initio Computation at UStc) is an open-source computer code package aiming for large-scale electronic-structure simulations from first principles, developed at the Key Laboratory of Quantum Information and Supercomputing Center, University of Science and Technology of China (USTC) - Computer Network and Information Center, Chinese of Academy (CNIC of CAS).

 ABACUS uses norm-conserving pseudopotentials to describe the interaction between nuclear ions and valence electrons. As its name indicates, ABACUS primarily employs numerically tabulated atom-centered orbitals as the basis functions to expand electronic wave functions. These basis functions are generated using an optimization scheme developed by Chen, Guo, and He(CGH) early on, and they form a series of hierarchical basis sets, through which the computational accuracy can be systematically improved. Besides atomic basis sets, ABACUS also offers the plane-wave basis set option. This dual basis-set feature allows for a convenient consistency accuracy check within ABACUS.

 ABACUS currently provides the following features and functionalities:

1.      Three types of supported basis sets: pw, LCAO, and LCAO-in-pw.

2.      Ground-state total energy calculations using Kohn-Sham (KS) density functional theory (DFT) with local-density, generalized gradient approximations (LDA/GGAs), Meta-GGA(requires LIBXC, only for PW), and hybrid functionals (PBE0 and HSE06, only for LCAO and currently under test).

3.      Geometry relaxations with Conjugated Gradient (CG), BFGS, and FIRE methods.

4.      Semi-empirical van der Waals energy correction using the Grimme DFT-D2/D3 scheme.

5.      NVT and NVE molecular dynamics simulation. AIMD, DP potential, LJ potential are supported.

6.      Stress calculations and cell relaxations.

7.      Electric polarization calculation using Berry Phase theory.

8.      Interface to the Wannier90 package.

9.      Real-time time dependent density functional theory (TDDFT).

10.    Print-out of the electrostatic potential.

11.    Mulliken charge analysis (only for LCAO).

12.    Projected density of states (PDOS) (only for LCAO).

13.    DFT+U calculation (only for LCAO).

14.    Solvation model method for solvation energy.

15.    Stochastic DFT (only for PW).

16.    DeePKS method (under development, only for LCAO).

17.    Electric field and dipole correction.

18.    Orbital-free DFT.

19.    (subsidiary tool)Plot_tools for plot PDOS and PBANDS.

20.    (subsidiary tool)Generator for second generation numerical orbital basis.

21.    Interface with DPGEN

22.    Interface with phonopy

23.    Implicit solvation model

Other functionalities including hybrid density functionals and spin-orbital coupling are under active development, and will be available in future releases.

ABACUS can run both on desktop computers and high performance supercomputers under the unix/linux-based environment. The code is massively parallelized, scaling up to O(10^3) CPU cores.