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# 1.3.9 New Features in Q-Chem 4.2

(February 4, 2022)
• Input file changes:

• New keyword METHOD simplifies input in most cases by replacing the pair of keywords EXCHANGE and CORRELATION (see Chapter 4).

• Keywords for requesting excited-state calculations have been modified and simplified (see Chapter 7 for details).

• Keywords for solvation models have been modified and simplified (see Section 11.2 for details).

• New features for NMR calculations including spin-spin couplings (J. Kussmann, A. Luenser, and C. Ochsenfeld; Section 10.11.2).

• New built-in basis sets (see Chapter 8).

• New features and performance improvements in EOM-CC:

• EOM-CC methods extended to treat meta-stable electronic states (resonances) via complex scaling and complex absorbing potentials (D. Zuev, T.-C. Jagau, Y. Shao, and A. I. Krylov; Section 7.10.9).

• New features added to EOM-CC iterative solvers, such as methods for interior eigenvalues and user-specified guesses (D. Zuev; Section 7.10.17).

• Multi-threaded parallel code for (EOM-)CC gradients and improved CCSD(T) performance.

• New features and performance improvements in ADC methods (M. Wormit, A. Dreuw):

• RI-ADC can tackle much larger systems at reduced cost (Section 7.11.4).

• SOS-ADC methods (Section 7.11.5).

• State-to-state properties for ADC (Section 7.11.9).

• SM12 implicit solvation model (A. V. Marenich, D. G. Truhlar, and Y. Shao; Section 11.2.9.1).

• Interface to NBO v. 6 (Section 10.3).

• Optimization of MECPs between electronic states at the SOS-CIS(D) and TDDFT levels (X. Zhang and J. M. Herbert; Section 9.8.3).

• ROKS method for $\Delta$SCF calculations of excited states (T. Kowalczyk and T. Van Voorhis; Section 7.8.2).

• Fragment-based initial guess for SCF methods (Section 12.3).

• Pseudo-fractional occupation number method for improved SCF convergence in small-gap systems (D. S. Lambrecht; Section 4.5.6).

• Density embedding scheme (B. J. Albrecht, E. Berquist, and D. S. Lambrecht; Section 11.6).

• New features and enhancements in fragment-based many-body expansion methods (K. U. Lao and J. M. Herbert):

• XSAPT(KS)+D: A dispersion corrected version of symmetry-adapted perturbation theory for fast and accurate calculation of interaction energies in non-covalent clusters (Section 12.14).

• Many-body expansion and fragment molecular orbital (FMO) methods for clusters (Section 12.16).

• Periodic boundary conditions with proper Ewald summation, for energies only (Z. C. Holden and J. M. Herbert; Section 11.3).