CHARMM (Chemistry at HARvard Molecular Mechanics) is a highly versatile and widely used molecu- lar simulation program. It has been developed over the last three decades with a primary focus on molecules of bio- logical interest, including proteins, peptides, lipids, nucleic acids, carbohydrates, and small molecule ligands, as they occur in solution, crystals, and membrane environments. For the study of such systems, the program provides a large suite of computational tools that include numerous conformational and path sampling methods, free energy estima- tors, molecular minimization, dynamics, and analysis techniques, and model-building capabilities. The CHARMM program is applicable to problems involving a much broader class of many-particle systems. Calculations with CHARMM can be performed using a number of different energy functions and models, from mixed quantum mechanical-molecular mechanical force fields, to all-atom classical potential energy functions with explicit solvent and various boundary conditions, to implicit solvent and membrane models. The program has been ported to numer- ous platforms in both serial and parallel architectures. This article provides an overview of the program as it exists today with an emphasis on developments since the publication of the original CHARMM article in 1983.

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CHARMM: the biomolecular simulation program.

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

A general scheme for systematically modeling long-range corrected (LC) hybrid density functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochemistry, kinetics, and noncovalent interactions, when compared with common hybrid density functionals. The qualitative failures of the commonly used hybrid density functionals in some “difficult problems,” such as dissociation of symmetric radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid density functionals.

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Systematic optimization of long-range corrected hybrid density functionals.

Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules.

Feshbach resonances in ultracold gases

Strong Closed-Shell Interactions in Inorganic Chemistry.

Theoretical studies of van der Waals molecules and intermolecular forces

We produce ultracold dense trapped samples of ^{87}Rb^{133}Cs molecules in their rovibrational ground state, with full nuclear hyperfine state control, by stimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We observe the onset of hyperfine-changing collisions when the magnetic field is ramped so that the molecules are no longer in the hyperfine ground state. A strong quadratic shift of the transition frequencies as a function of applied electric field shows the strongly dipolar character of the RbCs ground-state molecule. Our results open up the prospect of realizing stable bosonic dipolar quantum gases with ultracold molecules.

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Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state.

We report the creation of a sample of over 1000 ultracold $^{87}\mathrm{Rb}^{133}\mathrm{Cs}$ molecules in the lowest rovibrational ground state, from an atomic mixture of $^{87}\mathrm{Rb}$ and $^{133}\mathrm{Cs}$, by magnetoassociation on an interspecies Feshbach resonance followed by stimulated Raman adiabatic passage (STIRAP). We measure the binding energy of the RbCs molecule to be $hc\ifmmode\times\else\texttimes\fi{}3811.576(1)\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ and the $|{v}^{\ensuremath{'}\ensuremath{'}}=0,{J}^{\ensuremath{'}\ensuremath{'}}=0⟩$ to $|{v}^{\ensuremath{'}\ensuremath{'}}=0,{J}^{\ensuremath{'}\ensuremath{'}}=2⟩$ splitting to be $h\ifmmode\times\else\texttimes\fi{}2940.09(6)\text{ }\text{ }\mathrm{MHz}$. Stark spectroscopy of the rovibrational ground state yields an electric dipole moment of 1.225(3)(8) D, where the values in parentheses are the statistical and systematic uncertainties, respectively. We can access a space-fixed dipole moment of 0.355(2)(4) D, which is substantially higher than in previous work.

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Creation of ultracold ^{87}Rb^{133}Cs molecules in the rovibrational ground state.

A new intermolecular potential for Ar–HF is obtained by fitting to results from high‐resolution microwave, far‐infrared, and infrared spectroscopy. The new potential, designated H6(4,3,2), is a function of the diatom mass‐reduced vibrational quantum number η=(v+ (1)/(2) )/(μHX)1/2 as well as the intermolecular distance R and angle θ, and has 22 adjustable parameters. It reproduces all the available spectroscopic data for levels of Ar–HF correlating with HF, v=0, 1, and 2, and DF, v=0 and 1. The H6(4,3,2) potential is qualitatively similar to previous potentials, with a linear Ar–H–F equilibrium geometry and a secondary minimum at the linear Ar–F–H geometry. Compared to the potential of Nesbitt et al. [J. Chem. Phys. 90, 4855 (1989)], obtained from spectra of Ar–HF (v=1), the H6(4,3,2) potential is rather deeper near the equilibrium geometry (Ar–H–F), but shallower around the secondary minimum (Ar–F–H). The absolute well depth increases by 19 cm−1 between HF v=0 and v=1. The vibrationally averaged inductio...

Jeremy M. Hutson

Papers

Theoretical studies of van der Waals molecules and intermolecular forces

Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state.

Creation of ultracold ^{87}Rb^{133}Cs molecules in the rovibrational ground state.

Vibrational dependence of the anisotropic intermolecular potential of Ar–HF

Intermolecular Forces from the Spectroscopy of Van Der Waals Molecules