The PIAdressIntegrator implements the integration method for Hamiltonian Adaptive Resolution Path Integral Simulations proposed in J. Chem. Phys 147, 244104 (2017) (PI-AdResS). It can be used to run path integral molecular dynamics as well as ring polymer and centroid molecular dynamics in a quantum-classical adaptive resolution fashion, using different empirical force fields. To facilitate an efficient integration, the integrator uses a 3-layer RESPA (J. Chem. Phys. 97, 1990 (1992)) multiple timestepping scheme (inner level: intraatomic spring forces between the Trotter beads. medium level: interatomic bonded forces. outer level: interatomic non-bonded forces). Importantly, the integrator should only be used in combination with PI-AdResS interactions. Furthermore, the integrator has its own thermostat (Langevin), and the only extensions that should be used with it are the Free Energy Compensation (FreeEnergyCompensation) and the Thermodynamic Force (TDforce).

Example:

>>> integrator = espressopp.integrator.PIAdressIntegrator(system, verletlist, timestep_short, timesteps_outerlevel, timesteps_centrallevel, nTrotter, realkinmass, constkinmass, temperature, gamma, centroidthermostat, CMDparameter, PILE, PILElambda, clmassmultiplier, speedupFreezeRings, KTI)
>>> ...
>>> integrator.run(nsteps)

espressopp.integrator.PIAdressIntegrator(system, verletlist, timestep, sSteps, mSteps, nTrotter, realKinMass, constKinMass, temperature, gamma, centroidThermostat, CMDparameter, PILE, PILElambda, CLmassmultiplier, speedup, KTI)

Constructs the PIAdressIntegrator object. Note that all parameters can also be set and fetched via setter and getter functions. Additionally, all parameters except the system and the Verletlist are implemented as class variables that can be directly accessed and modified.

Parameters: system (shared_ptr) – system object verletlist (shared_ptr) – Verletlist object. Should be an AdResS Verletlist timestep (real) – (default: 0.0) the inner (shortest) timestep for the calculation of the intraatomic spring forces between the Trotter beads sSteps (int) – (default: 1) multiplier to construct medium timestep (interatomic bonded forces) as mediumstep = sSteps * timestep mSteps (int) – (default: 1) multiplier to construct longest timestep (interatomic non-bonded forces) as longstep = mSteps * sSteps * timestep nTrotter (int) – (default: 32) Trotter number. Should be even and greather than zero. realKinMass (bool) – (default: True) Flag to choose whether to use real kinetic masses. If False, the higher modes’ kinetic masses are multiplied with their corresponding eigenvalues of the normal mode transformation. In this way, all higher modes oscillate with the same frequency. If True, we use the kinetic masses for the higher modes which corresponding to the real dynamics (see J. Chem. Phys 147, 244104 (2017) for details) constKinMass (bool) – (default: False) If False, the higher modes’ kinetic masses also adaptively change (AKM scheme in J. Chem. Phys 147, 244104 (2017)). If True, the higher modes’ kinetic masses are constant throughout the system (CKM scheme in J. Chem. Phys 147, 244104 (2017)) temperature (real) – (default: 2.494353 - this corresponds to 300 Kelvin) the temperature in gromacs units (Boltzmann constant kb is 1) gamma (real) – (default: 1.0) the Langevin thermostat’s friction parameter in 1/ps centroidThermostat (bool) – (default: True) If True, the centroid mode is also thermostated, otherwise only the higher modes’ (relevant for centroid molecular dynamics) CMDparameter (real) – (default: 1.0) The gamma^2 parameter used in centroid molecular dynamics. The higher modes’ kinetic masses are rescaled by CMDparameter PILE (bool) – (default: True) If True, the higher modes are thermostated according to the PILE scheme by Ceriotti et al. (J. Chem. Phys 133, 124104 (2010)). Only makes sense in combination when using real kinetic masses (realKinMass = True) PILElambda (real) – (default: 0.5) lambda parameter to rescale the friction matrix. Default should be good for most applications (J. Chem. Phys 140, 234116 (2014)) CLmassmultiplier (real) – (default: 100.0) multiplier by which the higher modes’ spring masses (if constKinMass = False also the kinetic masses) are increased in the classical region speedup (bool) – (default: True) If True, the higher modes’ are not integrated in the classical region and also the intraatomistic forces between the Trotter beads are not calculated in the classical region KTI (bool) – (default: False) If True, the particles’ resolution parameters and adaptive masses are not updated but can be set by hand everywhere. This is necessary when running Kirkwood Thermodynamic Integration (KTI)
espressopp.integrator.PIAdressIntegrator.setVerletList(verletlist)

Sets the VerletList.

espressopp.integrator.PIAdressIntegrator.getVerletList()

Gets the VerletList.

espressopp.integrator.PIAdressIntegrator.setTimeStep(timestep)

Sets the inner (shortest) timestep.

Parameters: timestep (real) – the inner timestep
espressopp.integrator.PIAdressIntegrator.getTimeStep()

Gets the inner (shortest) timestep.

Returns: the inner timestep real
espressopp.integrator.PIAdressIntegrator.setsStep(sSteps)

Sets the multiplier to construct medium timestep (interatomic bonded forces) as mediumstep = sSteps * timestep.

Parameters: sSteps (int) – multiplier to construct medium timestep
espressopp.integrator.PIAdressIntegrator.getsStep()

Gets the multiplier to construct medium timestep (interatomic bonded forces) as mediumstep = sSteps * timestep.

Returns: multiplier to construct medium timestep int
espressopp.integrator.PIAdressIntegrator.setmStep(mSteps)

Sets the multiplier to construct longest timestep (interatomic non-bonded forces) as longstep = mSteps * sSteps * timestep.

Parameters: mSteps (int) – multiplier to construct longest timestep
espressopp.integrator.PIAdressIntegrator.getmStep()

Gets the multiplier to construct longest timestep (interatomic non-bonded forces) as longstep = mSteps * sSteps * timestep.

Returns: multiplier to construct longest timestep int
espressopp.integrator.PIAdressIntegrator.setNtrotter(nTrotter)

Sets the Trotter number nTrotter. Should be even and greather than zero. Note that when calling this function, also the normal mode transformation matrix and the eigenvalues are recalculated.

Parameters: ntrotter (int) – the Trotter number
espressopp.integrator.PIAdressIntegrator.getNtrotter()

Gets the Trotter number nTrotter.

Returns: the Trotter number int
espressopp.integrator.PIAdressIntegrator.setRealKinMass(realKinMass)

Sets the real kinetic mass flag.

Parameters: realKinMass (bool) – the real kinetic mass flag
espressopp.integrator.PIAdressIntegrator.getRealKinMass()

Gets the real kinetic mass flag.

Returns: the real kinetic mass flag bool
espressopp.integrator.PIAdressIntegrator.setConstKinMass(constKinMass)

Sets the constant kinetic mass flag.

Parameters: constKinMass (bool) – the constant kinetic mass flag
espressopp.integrator.PIAdressIntegrator.getConstKinMass()

Gets the constant kinetic mass flag.

Returns: the constant kinetic mass flag bool
espressopp.integrator.PIAdressIntegrator.setTemperature(temperature)

Sets the temperature (gromacs units with kb = 1).

Parameters: temperature (real) – the temperature
espressopp.integrator.PIAdressIntegrator.getTemperature()

Gets the temperature (gromacs units with kb = 1).

Returns: the temperature real
espressopp.integrator.PIAdressIntegrator.setGamma(gamma)

Sets the friction constant gamma (in 1/ps).

Parameters: gamma (real) – the friction constant gamma
espressopp.integrator.PIAdressIntegrator.getGamma()

Gets the friction constant gamma (in 1/ps).

Returns: the friction constant gamma real
espressopp.integrator.PIAdressIntegrator.setCentroidThermostat(centroidThermostat)

Sets the centroid thermostat flag.

Parameters: centroidThermostat (bool) – the centroid thermostat flag
espressopp.integrator.PIAdressIntegrator.getCentroidThermostat()

Gets the centroid thermostat flag.

Returns: the centroid thermostat flag bool
espressopp.integrator.PIAdressIntegrator.setCMDparameter(CMDparameter)

Sets the centroid molecular dynamics parameter gamma^2 for scaling the kinetic mass.

Parameters: CMDparameter (real) – the CMD parameter gamma^2
espressopp.integrator.PIAdressIntegrator.getCMDparameter()

Gets the centroid molecular dynamics parameter gamma^2 for scaling the kinetic mass.

Returns: the CMD parameter gamma^2 real
espressopp.integrator.PIAdressIntegrator.setPILE(PILE)

Sets the PILE flag.

Parameters: PILE (bool) – the PILE flag
espressopp.integrator.PIAdressIntegrator.getPILE()

Gets the PILE flag.

Returns: the PILE flag bool
espressopp.integrator.PIAdressIntegrator.setPILElambda(PILElambda)

Sets the scaling parameter lambda of the PILE thermostat.

Parameters: PILElambda (real) – the scaling parameter lambda
espressopp.integrator.PIAdressIntegrator.getPILElambda()

Gets the scaling parameter lambda of the PILE thermostat.

Returns: the scaling parameter lambda real
espressopp.integrator.PIAdressIntegrator.setClmassmultiplier(CLmassmultiplier)

Sets the multiplier for the higher modes’ spring masses in the classical region.

Parameters: CLmassmultiplier (real) – the classical spring mass multiplier
espressopp.integrator.PIAdressIntegrator.getClmassmultiplier()

Gets the multiplier for the higher modes’ spring masses in the classical region.

Returns: the classical spring mass multiplier real
espressopp.integrator.PIAdressIntegrator.setSpeedup(speedup)

Sets the speedup flag.

Parameters: speedup (bool) – the speedup flag
espressopp.integrator.PIAdressIntegrator.getSpeedup()

Gets the speedup flag.

Returns: the speedup flag bool
espressopp.integrator.PIAdressIntegrator.setKTI(KTI)

Sets the KTI flag.

Parameters: speedup (bool) – the KTI flag
espressopp.integrator.PIAdressIntegrator.getKTI()

Gets the KTI flag.

Returns: the KTI flag bool
espressopp.integrator.PIAdressIntegrator.getVerletlistBuilds()

Gets the number of Verletlist builds.

Returns: number of Verletlist builds int
espressopp.integrator.PIAdressIntegrator.computeRingEnergy()

Calculates the total configurational energy of all ring polymers in the system based on the springs between the Trotter beads (calculation done using mode coordinates).

Returns: total configurational ring polymer energy real
espressopp.integrator.PIAdressIntegrator.computeRingEnergyRaw()

Calculates the total configurational energy of all ring polymers in the system based on the springs between the Trotter beads (calculation done using the Trotter beads’ real space positions).

Returns: total configurational ring polymer energy real
espressopp.integrator.PIAdressIntegrator.computeKineticEnergy()

Calculates the total kinetic energy using the modes’ momenta.

Returns: total kinetic energy real
espressopp.integrator.PIAdressIntegrator.computePositionDrift(parttype)

Calculates the average drift force due to the position-dependent spring masses (see Section 5.C. Eq. 63 in J. Chem. Phys 147, 244104 (2017)) on particles of type parttype. To be used during KTI for construction of free energy compensation.

Parameters: parttype (int) – the particle or atom type average drift force due to the position-dependent spring masses real
espressopp.integrator.PIAdressIntegrator.computeMomentumDrift(parttype)

Calculates the average drift force due to the position-dependent kinetic masses (see Section 5.C. Eq. 62 in J. Chem. Phys 147, 244104 (2017)) on particles of type parttype. To be used during KTI for construction of free energy compensation.

Parameters: parttype (int) – the particle or atom type average drift force due to the position-dependent kinetic masses real
class espressopp.integrator.PIAdressIntegrator.PIAdressIntegratorLocal(system, verletlist, timestep=0.0, sSteps=1, mSteps=1, nTrotter=32, realKinMass=True, constKinMass=False, temperature=2.494353, gamma=1.0, centroidThermostat=True, CMDparameter=1.0, PILE=True, PILElambda=0.5, CLmassmultiplier=100.0, speedup=True, KTI=False)