# pair_style oxrna2/dh command

## Syntax

pair_style style1

pair_coeff * * style2 args

• style1 = hybrid/overlay oxrna2/excv oxrna2/stk oxrna2/hbond oxrna2/xstk oxrna2/coaxstk oxrna2/dh

• style2 = oxrna2/excv or oxrna2/stk or oxrna2/hbond or oxrna2/xstk or oxrna2/coaxstk or oxrna2/dh

• args = list of arguments for these particular styles

oxrna2/stk args = seq T xi kappa 6.0 0.43 0.93 0.35 0.78 0.9 0 0.95 0.9 0 0.95 1.3 0 0.8 1.3 0 0.8 2.0 0.65 2.0 0.65
seq = seqav (for average sequence stacking strength) or seqdep (for sequence-dependent stacking strength)
T = temperature (oxDNA units, 0.1 = 300 K)
xi = 1.40206 (temperature-independent coefficient in stacking strength)
kappa = 2.77 (coefficient of linear temperature dependence in stacking strength)
oxrna2/hbond args = seq eps 8.0 0.4 0.75 0.34 0.7 1.5 0 0.7 1.5 0 0.7 1.5 0 0.7 0.46 3.141592653589793 0.7 4.0 1.5707963267948966 0.45 4.0 1.5707963267948966 0.45
seq = seqav (for average sequence base-pairing strength) or seqdep (for sequence-dependent base-pairing strength)
eps = 0.870439 (between base pairs A-T, C-G and G-T) or 0 (all other pairs)
oxrna2/dh args = T rhos qeff
T = temperature (oxDNA units, 0.1 = 300 K)
rhos = salt concentration (mole per litre)
qeff = 1.02455 (effective charge in elementary charges)

## Examples

pair_style hybrid/overlay oxrna2/excv oxrna2/stk oxrna2/hbond oxrna2/xstk oxrna2/coaxstk oxrna2/dh
pair_coeff * * oxrna2/excv    2.0 0.7 0.675 2.0 0.515 0.5 2.0 0.33 0.32
pair_coeff * * oxrna2/stk     seqdep 0.1 1.40206 2.77 6.0 0.43 0.93 0.35 0.78 0.9 0 0.95 0.9 0 0.95 1.3 0 0.8 1.3 0 0.8 2.0 0.65 2.0 0.65
pair_coeff * * oxrna2/hbond   seqdep 0.0 8.0 0.4 0.75 0.34 0.7 1.5 0 0.7 1.5 0 0.7 1.5 0 0.7 0.46 3.141592653589793 0.7 4.0 1.5707963267948966 0.45 4.0 1.5707963267948966 0.45
pair_coeff 1 4 oxrna2/hbond   seqdep 0.870439 8.0 0.4 0.75 0.34 0.7 1.5 0 0.7 1.5 0 0.7 1.5 0 0.7 0.46 3.141592653589793 0.7 4.0 1.5707963267948966 0.45 4.0 1.5707963267948966 0.45
pair_coeff 2 3 oxrna2/hbond   seqdep 0.870439 8.0 0.4 0.75 0.34 0.7 1.5 0 0.7 1.5 0 0.7 1.5 0 0.7 0.46 3.141592653589793 0.7 4.0 1.5707963267948966 0.45 4.0 1.5707963267948966 0.45
pair_coeff 3 4 oxrna2/hbond   seqdep 0.870439 8.0 0.4 0.75 0.34 0.7 1.5 0 0.7 1.5 0 0.7 1.5 0 0.7 0.46 3.141592653589793 0.7 4.0 1.5707963267948966 0.45 4.0 1.5707963267948966 0.45
pair_coeff * * oxrna2/xstk    59.9626 0.5 0.6 0.42 0.58 2.25 0.505 0.58 1.7 1.266 0.68 1.7 1.266 0.68 1.7 0.309 0.68 1.7 0.309 0.68
pair_coeff * * oxrna2/coaxstk 80 0.5 0.6 0.42 0.58 2.0 2.592 0.65 1.3 0.151 0.8 0.9 0.685 0.95 0.9 0.685 0.95 2.0 -0.65 2.0 -0.65
pair_coeff * * oxrna2/dh      0.1 0.5 1.02455


## Description

The oxrna2 pair styles compute the pairwise-additive parts of the oxDNA force field for coarse-grained modelling of DNA. The effective interaction between the nucleotides consists of potentials for the excluded volume interaction oxrna2/excv, the stacking oxrna2/stk, cross-stacking oxrna2/xstk and coaxial stacking interaction oxrna2/coaxstk, electrostatic Debye-Hueckel interaction oxrna2/dh as well as the hydrogen-bonding interaction oxrna2/hbond between complementary pairs of nucleotides on opposite strands. Average sequence or sequence-dependent stacking and base-pairing strengths are supported (Sulc2). Quasi-unique base-pairing between nucleotides can be achieved by using more complementary pairs of atom types like 5-8 and 6-7, 9-12 and 10-11, 13-16 and 14-15, etc. This prevents the hybridization of in principle complementary bases within Ntypes/4 bases up and down along the backbone.

The exact functional form of the pair styles is rather complex. The individual potentials consist of products of modulation factors, which themselves are constructed from a number of more basic potentials (Morse, Lennard-Jones, harmonic angle and distance) as well as quadratic smoothing and modulation terms. We refer to (Sulc1) and the original oxDNA publications (Ouldridge-DPhil) and (Ouldridge) for a detailed description of the oxRNA2 force field.

Note

These pair styles have to be used together with the related oxDNA2 bond style oxrna2/fene for the connectivity of the phosphate backbone (see also documentation of bond_style oxrna2/fene). Most of the coefficients in the above example have to be kept fixed and cannot be changed without reparameterizing the entire model. Exceptions are the first four coefficients after oxrna2/stk (seq=seqdep, T=0.1, xi=1.40206 and kappa=2.77 in the above example), the first coefficient after oxrna2/hbond (seq=seqdep in the above example) and the three coefficients after oxrna2/dh (T=0.1, rhos=0.5, qeff=1.02455 in the above example). When using a Langevin thermostat e.g. through fix langevin or fix nve/dotc/langevin the temperature coefficients have to be matched to the one used in the fix.

Example input and data files for DNA duplexes can be found in examples/USER/cgdna/examples/oxDNA/ and /oxDNA2/. A simple python setup tool which creates single straight or helical DNA strands, DNA duplexes or arrays of DNA duplexes can be found in examples/USER/cgdna/util/.

Please cite (Henrich) in any publication that uses this implementation. The article contains general information on the model, its implementation and performance as well as the structure of the data and input file. The preprint version of the article can be found here. Please cite also the relevant oxRNA2 publications (Sulc1) and (Sulc2).

## Restrictions

These pair styles can only be used if LAMMPS was built with the USER-CGDNA package and the MOLECULE and ASPHERE package. See the Build package doc page for more info.