New features:
* DFT-D3 interface
* semi_incore ao2mo transformation
* PBC k-point SCF stability analysis
* PBC KUCCSD
* PBC EOM-IP/EA-KRCCSD
* PBC EOM-IP/EA-KUCCSD
* X2C-UKS (LDA functional only)
* PBC gamma point ROHF/ROKS and GKS
* PBC KROHF/KROKS and KGKS for k-point sampling
* DFT Coulomb and XC integrals with multigrid
* Periodic UCCSD with k-point sampling
* perturbative DMRG method
* Interface to Cornell SHCI
* PBC dipole memont and Makov-Payne correction
* Overlap of two CISD wavefunctions
* EFG and Mossbauer spectroscopy of crystal and molecule
* Molecular magnetizability for HF and DFT
* ddCOSMO and ddPCM for MCSCF, MP, CI and CC methods
* Non-relativistic static and dynamic polarizability and hyper-polarizability tensor
Improvements:
* Linear dependency threshold of qr decomposition in davidson solver
* Optimized KUCCSD, EOM-KUCCSD performance
* numint performance (eval_rho, eval_mat)
* Energy cutoff estimation
* The treatment of HF exchange in PBC system when calling PBC MP2, CISD, CCSD code
* Convergence performance of KCCSD iterations for low-dimension systems
* CCSD convergency for 2D-PBC AFTDF, GDF and MDF methods
* Integral transformation performance in GW
* Molden parser to handel UHF orbitals
* IO performance of pbc.GDF initialization
* Default linear dependence treatment in GDF to improve accuracy
* The memory usage for a large number of MM particles (issue 193)
Bugfix:
* hasattr issue for attributes with property
* DDCOSMO wrapper and kernel function
* Num eletrons bug in PBC smearing function for custom systems
* return value of NPTaggedArray ufunc (returning np array now)
* PBC density fitting dimension error caused by numerical noise when handling linear dependency
* Parsers for molpro basis and gaussian basis
* Selected-CI returned data type
* Complex density in pbc.get_j function
* Get_fermi in KHF and KUHF
* Execute call in dmrgci
* Directories and paths in dmrgci
* Read of 3-pdm and 4-pdm produced by block-1.5
* Initialization wrapper in pbc.scf.__init__
* Complex density in pbc.get_j function
* Get_fermi in KHF and KUHF
* Execute call in dmrgci
* Directories and paths in dmrgci
* Read of 3-pdm and 4-pdm produced by block-1.5
* Initialization wrapper in pbc.scf.__init__
* Complex density in pbc.get_j function
* Initial guess of KROHF method
* PBC get_jk interface when calling molecular MCSCF with pbc scf object
* keyword argument with_df of pbc.dft density_fit wrapper
* OpenMP race condition in FCI solver
* Undefined HDF5 dataset in PBC MDF initialization
* TD-KRHF vind function
* SCF hessian
* interface between DMRG-CI and DMRG-NEVPT2. Making DMRG-NEVPT2 read Block code settings in DMRG-CI.
* Dimension error in pbc.fftdf.get_jk for KUHF density matrix
* pbc.mpicc for keyword frozen
* Periodic pseudopotential calculations with ghost atoms
* get_jk prescreen for non-hermitian density matrices.
* Inaccurate estimation of memory usage in ccsd rdm.
* Frozen orbital EA-EOM-KRCCSD
* IOError due to 4GB chunk size limit in HDF5 library
* Selected-ci 2-particle density matrices for two-electron systems
* Frozen orbitals in MCSCF canonicalization
* Dimension error when initializing DF-CCSD integral tensor
* EOM-EE-UCCSD initial guess and intermediates (issue 199)
* mpi ip/eaccsd w/ frozen orbitals
* the tdscf.get_nto function when mol.symmetry is enabled (issue 196)
* the interface between QMMM wrapper and the gradients of post-HF methods
See also the [release notes](https://github.com/pyscf/pyscf/blob/master/doc/whatsnew/1.6.rst)
This release contains contributions from:
Qiming Sun, James. D. McClain, Peter Koval, Marc Barbry, Jason Yu, Cao Yang, Mario Motta, Alec White, Artem Pulkin, Timothy Berkelbach,Nikolay Bogdanov, Janus Juul Eriksen, Huang Pham, Chong Sun, Shining Sun, Matthew Hermes, Henry Schurkus, Matthew Chan, James D. Whitfield, Bastien Mussard