AMBER

For other uses, see Amber (disambiguation).
AMBER is used to minimize the bond stretching energy of this ethane molecule.

AMBER (an acronym for Assisted Model Building with Energy Refinement) is a family of force fields for molecular dynamics of biomolecules originally developed by Peter Kollman's group at the University of California, San Francisco. AMBER is also the name for the molecular dynamics software package that simulates these force fields. It is maintained by an active collaboration between David Case at Rutgers University, Tom Cheatham at the University of Utah, Tom Darden at NIEHS, Ken Merz at Michigan State University, Carlos Simmerling at Stony Brook University, Ray Luo at UC Irvine, and Junmei Wang at Encysive Pharmaceuticals.

Force field

The term "AMBER force field" generally refers to the functional form used by the family of AMBER force fields. This form includes a number of parameters; each member of the family of AMBER force fields provides values for these parameters and has its own name.

Functional form

The functional form of the AMBER force field is[1]

V(r^{N})=\sum _{\text{bonds}}k_{b}(l-l_{0})^{2}+\sum _{\text{angles}}k_{a}(\theta -\theta _{0})^{2}

+\sum _{\text{torsions}}\sum _{n}{\frac {1}{2}}V_{n}[1+\cos(n\omega -\gamma )] +\sum _{j=1}^{N-1}\sum _{i=j+1}^{N}f_{ij}{\biggl \{}\epsilon _{ij}{\biggl [}\left({\frac {r_{0ij}}{r_{ij}}}\right)^{12}-2\left({\frac {r_{0ij}}{r_{ij}}}\right)^{6}{\biggr ]}+{\frac {q_{i}q_{j}}{4\pi \epsilon _{0}r_{ij}}}{\biggr \}}

Note that despite the term force field, this equation defines the potential energy of the system; the force is the derivative of this potential with respect to position.

The meanings of right hand side terms are:

The form of the van der Waals energy is calculated using the equilibrium distance (r_{0ij}) and well depth (\epsilon ). The factor of 2 ensures that the equilibrium distance is r_{0ij}. The energy is sometimes reformulated in terms of \sigma , where r_{0ij}=2^{1/6}(\sigma ), as used e.g. in the implementation of the softcore potentials.

The form of the electrostatic energy used here assumes that the charges due to the protons and electrons in an atom can be represented by a single point charge (or in the case of parameter sets that employ lone pairs, a small number of point charges.)

Parameter sets

To use the AMBER force field, it is necessary to have values for the parameters of the force field (e.g. force constants, equilibrium bond lengths and angles, charges). A fairly large number of these parameter sets exist, and are described in detail in the AMBER software user manual. Each parameter set has a name, and provides parameters for certain types of molecules.

Software

The AMBER software suite provides a set of programs for applying the AMBER forcefields to simulations of biomolecules. It is written in Fortran 90 and C with support for most major Unix-like systems and compilers. Development is conducted by a loose association of mostly academic labs. New versions are generally released in the spring of even numbered years; AMBER 10 was released in April 2008. The software is available under a site-license agreement, which includes full source, currently priced at US$500 for non-commercial and US$20,000 for commercial organizations.

Programs

See also

References

  1. Cornell WD, Cieplak P, Bayly CI, Gould IR, Merz KM Jr, Ferguson DM, Spellmeyer DC, Fox T, Caldwell JW, Kollman PA (1995). "A Second Generation Force Field for the Simulation of Proteins, Nucleic Acids, and Organic Molecules". J. Am. Chem. Soc. 117: 5179–5197. doi:10.1021/ja00124a002.

Further reading

External links

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