Workshop -- to the Workshop -- Quantum Systems in Chemistry and Physics XIIth Workshop Report -- Proceedings -- Study of the Electronic Structure of the Unconventional Superconductor Sr2RuO4 by the Embedded Cluster Method -- An Introduction to the Density Matrix Renormalization Group Ansatz in Quantum Chemistry -- Method of Moments of Coupled Cluster Equations Employing Multi-Reference Perturbation Theory Wavefunctions: General Formalism, Diagrammatic Formulation, Implementation, and Benchmark Studies -- Guidelines on the Contracted Schrödinger Equation Methodology -- Molecular Energy Decompositions in the Hilbert-Space of Atomic Orbitals at Correlated Level -- Dirac-Coulomb Equation: Playing with Artifacts -- Are Einstein's Laws of Relativity a Quantum Effect? -- Electron Correlation and Nuclear Motion Corrections to the Ground-State Energy of Helium Isoelectronic Ions from Li to Kr -- Unusual Features in Optical Absorption and Photo-Ionisation of Quantum Dot Nano-Rings -- Relative Energies of Proteins and Water Clusters Predicted with the Generalized Energy-Based Fragmentation Approach -- Generalised Spin Dynamics and Induced Bounds of Automorphic [A]nX, [AX]n NMR Systems via Dual Tensorial Sets: An Invariant Cardinality Role for CFP -- The Macroscopic Quantum Behavior of Protons in the KHCO3 Crystal: Theory and Experiments -- A DFT Study of Adsorption of Gallium and Gallium Nitrides on Si(111) -- Viscosity of Liquid Water via Equilibrium Molecular Dynamics Simulations -- Stochastic Description of Activated Surface Diffusion with Interacting Adsorbates -- Interactions and Collision Dynamics in O2 + O2 -- The Non-Adiabatic Molecular Hamiltonian: A Derivation Using Quasiparticle Canonical Transformations -- Alternative Technique for the Constrained Variational Problem Based on an Asymptotic Projection Method: I. Basics -- Alternative Technique for the Constrained Variational Problem Based on an Asymptotic Projection Method: II. Applications to Open-Shell Self-Consistent Field Theory -- SU(m(? 4)) × l20 ? A5 Group Branching Rules Revisited: Inverse Polyhedral Combinatorial Modelling via (?) to {} ? ?SASST Maps -- Gauge-Invariant QED Perturbation Theory Approach to Calculating Nuclear Electric Quadrupole Moments, Hyperfine Structure Constants for Heavy Atoms and Ions -- New Laser-Electron Nuclear Effects in the Nuclear ? Transition Spectra in Atomic and Molecular Systems -- QED Approach to Atoms in a Laser Field: Multi-Photon Resonances and Above Threshold Ionization -- A Collaborative Virtual Environment for Molecular Electronic Structure Theory: A Prototype for the Study of Many-Body Methods.