Low Scaling Quantum Chemistry (LSQC) Program  
1. Introduction Low Scaling Quantum Chemistry (LSQC) program is a quantum chemistry package for linear or low scaling electronic structure calculations of large systems, which is developed by the research group of Professor Shuhua Li and Professor Wei Li in Nanjing University. The original version is LSQC1.0 published on April 20, 2006, and the current version is LSQC2.4 published on October 1, 2019. Current LSQC program supports two methods developed by Li group. The first one is the generalized energybased fragmentation (GEBF) method and the other one is the clusterinmolecule (CIM) local correlation method. Both methods can achieve linear scaling for electronic structure calculations of large systems and have high parallel efficiency. 2. License and Documentation
3. Modules (1) Generalized energybased fragmentation (GEBF) approach Within the GEBF approach, the total energy of a macromolecule can be directly obtained from the energies of a series of subsystems, which can be obtained from running conventional quantum chemistry calculations. The approach can lead to good results for closeshell systems with localized electrons, such as biomolecules and polymers. For systems with hundreds and even thousands of atoms, the GEBFX approach allows full quantum mechanical (QM) calculations at the X level to be accessible on ordinary workstations. The calculations of electrostatically embedded subsystems at various theoretical levels can be done with existing quantum chemistry programs. In this version, only Gaussian program is supported for subsystem calculations. The single point calculation (SP) at semiempirical method (AM1, PM3, PM6, etc), HF, DFT and electronic correlation method (MP2, MP3, MP4, CCSD, CCSD(T)) is available in current version. And the geometry optimization (Opt), frequency (Freq), IR intensity, Raman intensity, zeropoint energy, enthalpy, Gibbs free energy, dipole moment, static polarizability, hyperpolarizability and NMR are also available in this version. (2) Clusterinmolecule (CIM) approach Within the CIM approach, electronic correlation equations are solved within the representation of occupied and virtual localized molecular orbitals. For a target molecule, the clusters are built from localized molecular orbitals automatically by the program. The approximate correlation energy of the target molecule is obtained from the correlation energy contributions of a series of clusters, which are solved independently. Single point energy at CIMMP2 and CIMRIMP2 levels is available in current version. In addition, conventional MP2 and RIMP2 calculations for mediumsized systems are also supported. 4. References All publications resulting from use of this program must cite the following two references.
Depending on which programs are used, the following references should be cited. GEBF approach: All publications calculated with GEBF module should cite the following references: The license of Gaussian should be available for you and cited if Gaussian program is employed for subsystems calculations. See http://www.gaussian.com/ for more information. For specific methods, more references should be cited as follows: CIM approach: The following references should be cited if the CIM approach is used: In the present version, HartreeFock calculations are performed by the PySCF package and the electron integrals are used Libcint electron integral library. The reference are:
