CHARMM Element doc/mts.doc 1.1#File: MTS, Node: Top, UP: (chmdoc/dynamc.doc), Previous: (chmdoc/dynamc.doc), Next: Syntax **************************************** * Multiple Time Scales Method (MTS) * **************************************** In CHARMM, multiple time scales method (MTS) algorithm is similarto code of the algorithm described in the paper by Tuckerman, Berne,and Martyna [J.C.P., 97, 1990 (1992)]. Please refer to this paper for details of derivations of this MTS-RESPA method. In addtion, more details can be seen in J. Chem. Phys. 99, 8063 (1993) and J. Phys. Chem., 99, 5680 (1995) by M. Watanabe and M. Karplus. In this new release, MTS method canbe called under parallel platforms. All modules under MTS should work inparallel. To run CHARMM in parallel, please refer to parallel.doc. The MTS method can be combined with Langevin dynamics via theLN algorithm, described by Barth and Schlick [J.Chem.Phys., 1998, in press].This version includes the slow forces via extrapolation and is expected toallow larger timesteps than reversible MTS-RESPA. Seegeneral notes at the end of this documentation file.LN algorithm was implemented in CHARMM by Eric Barth (8/97) andAdrian Sandu (7/98). In this documentation we refer to the rRESPA code as MTS-RESPA(performing Newtonian dynamics) and to the LN code as MTS-LN(performing Langevin dynamics). *Menu:* Syntax:: Syntax of the MTS dynamics command* Desc:: Description of the keywords and options* Note:: Energy routines and MTS method selections * Exam:: Example of Multiple Time Scale Method#File: MTS, Node: Syntax, Up: Top, Next: Desc, Previous: Top **************************************************** * Syntax for the Multiple Time Scaled Method (MTS) * ****************************************************In this Multiple Time scaled method in CHARMM, a reversible RESPA(Reference System Propagator Algorithm) is modified. (See Tuckerman'spaper about a reversible RESPA.) Two types of reversible RESPA methodscan be used in CHARMM. 1) Single reversible RESPA (Two-time-scale propagator) MTSmethod 1 I mts-spec END I :: multiple time scales (Integer) - See Description mts-spec:: selection of hard forces or fast time scaled force [BOND] ! Forces from all Bond-stretching motions [ANGL] ! Forces from all angle-bending motions [DIHE] ! Forces from all diheral motions and all improper ! torsional motion [ALL ] ! Forces from all internal motions which are! defined in CHAMM force fields [MASS] 1 M ! Nonbonded forces involving atoms whose masses are ! less than M. M is a mass weight. [SLFG] ! Nonbonded forces separation by long- and short- ! range forces (see more detail in the text) [CLEA] ! Clear MTS module and assignments 2) Double reversible RESPA (Three-time-scale propagator) MTSmethod I J mts-spec END I and J :: multiple time scales (Integers) - See Description mts-spec:: selections of fast and medium time scaled forces [BOND] K ! Forces from all Bond-stretching motions [ANGL] K ! Forces from all angle-bending motions [DIHE] K ! Forces from all diheral motions and all improper ! torsional motion [ALL ] K ! Forces from all internal motions which are ! defined in CHAMM force fields [MASS] K M ! Nonbonded forces involving atoms whose masses are ! less than M. M is a mass weight. [SLFG] ! Nonbonded forces separation by long- and short- ! range forces (see more detail in the text) [CLEA] ! Clear MTS module and assignments K is 1 or 2 - 1 - force considered as a short time scaled 2 - force considered as a medium time scaled In both single and double RESPA methods, all interaciton forces, which are not selected by MTS command, are considered as a long time scaled degree of freedom You can see the more details in J. Chem. Phys. 99, 8063 (1993) and J. Phys. Chem., 99, 5680 (1995) by M. Watanabe and M. Karplus.3) MASS (Atomic Mass force separation) If MASS is selected, separating mass should be given. MTS . . MASS K M END K is the force considered as a short or medium time scaled. This should be 1 or 2 ( 1 for short and 2 for medium ) M is the atomic mass. Separate the force contributions by the atomic mass. Contributions from the atom less than M mass is considered as the faster time scaled motions than those from the atom more than M mass. See the more details about this in J. Phys. Chem. 99, 5680 (1995), by M. Watanabe and M. Karplus.4) SLFG (Short-Long Range force separation) If SLFG is selected, Short range force cutoff distance (RSCUT), switching function healing length (RHEA), and Buffer healing length (BUFF) should be given by the following way: MTS. SLFG RSCUT [number (6.0)] RHEA [number (1.0)] BUFF [number (1.0)] END [number] is the distance in the unit of Angstrom. (..) is the default values. See the more details about these lengths in J. Phys. Chem. 98, 6885, (1994) by D.D.Humphreys, R.A.Friesner, and B.J. Berne.#File: MTS, Node: Desc, Up: Top, Previous: Syntax, Next: Note ******************************************* * Description of MTS Dynamics Commands * *******************************************MTS method approach is effective for special system where a separationbetween the fast and slow time components is natural. The nature ofCHARMM force field allow us to separate some time scales. But in generthere will be coupling between those motions, so this leads thelimitation of time scales.a. In Multiple time scale, I and J are the number of cycle that you want to calculate short time scaled and medium time scaled motions, respectively, before calculating long time scaled motion. Delta t = J * Dtau2 = I * J * Dtau1 where Dtau1 and Dtau1 are the integral time step for short and medium time scaled motions respectively and Delta t is the integration time step of long time scaled motions. Dtau1 is defined in DYNAmic module as TIME.b. MTS-RESPA method uses the velocity Verlet algorithm. MTS-LN algorithm solves the simple Langevin equation and relies on