Overview of example use
This is an example workflow for doing the whole calculation, except calculating potential itself that has been explained else where.
Molecular dynamics itself consist of 4 phases:
- Equilibration of initial geometry in gas phase
- Condensing gas to solid.
- Equilibration to DFT
- Spectrum calculation
Fitting Potential
First we need to fit a potential. In this example we fit a potential for trans-formic acid and argon. PotentialDB has pre calculated data than we can use for fitting the potential.
using PotentialDB
r = defaultregistry()
data = loadpotential(r, "4")Dict{String, Any} with 6 entries:
"Method" => "CCSD(T)-F12/RI"
"cluster2" => Cluster{AtomOnlySymbol} of 1 atoms
"Energy" => [0.0172099 0.0232891 … 0.0210108 0.0160872; 0.0104979 0.0147825…
"Points" => Cluster{AtomOnlySymbol}[Cluster{AtomOnlySymbol} of 6 atoms Clus…
"cluster1" => Cluster{AtomOnlySymbol} of 5 atoms
"Basis" => "cc-pVDZ-F12 cc-pVDZ-F12-CABS cc-pVTZ/C TIGHTSCF"The fitting procedure is the same as explained in Usage section.
First we create a potential for fitting.
using PotentialFitting, PotentialCalculation
m1, m2 = get_molecules(data)
mpp = MoleculePairPotential(m1,m2, GeneralPowers(-6,-8,-10,-12,-7,-9,-11))Molecule Pair Potential
Molecule 1 has 5 atoms (5 unique)
Molecule 2 has 1 atoms (1 unique)
Potential topology:
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 0.0 0.0 0.0 0.0 0.0 0.0 0.0 : 1C : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 0.0 0.0 0.0 0.0 0.0 0.0 0.0 : 2O : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 0.0 0.0 0.0 0.0 0.0 0.0 0.0 : 3O : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 0.0 0.0 0.0 0.0 0.0 0.0 0.0 : 4H : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 0.0 0.0 0.0 0.0 0.0 0.0 0.0 : 5H : 6Ar
Then we prepare fitting data and apply some constrains. The reason why we applying constrains is that our potential is under fitting and as a result depends heavily on the constrains. You can verify this, by taking constrains off and comparing to constrained potential, or by changing the constrains considerably.
fdata = FitData(mpp, data["Points"], data["Energy"])
# setweight_e_more!(fdata, weight, minimum_energy)
setweight_e_more!(fdata, 0.1, 1000u"cm^-1")
setweight_e_more!(fdata, 0.01, 5000u"cm^-1")
setweight_e_less!(fdata, 2, -50u"cm^-1")
setweight_e_less!(fdata, 4, -75u"cm^-1")
setweight_e_less!(fdata, 16, -100u"cm^-1");Optional defining a model
Then we prepare fitting tools for fitting. Standard linear regression is most likely good enough. But you can try others as well.
Here we load LinearRegressor that does not fit intercept
using MLJ
LinearRegressor = @load LinearRegressor pkg=GLM
model = LinearRegressor(fit_intercept=false)LinearRegressor(
fit_intercept = false,
dropcollinear = false,
offsetcol = nothing,
report_keys = [:deviance, :dof_residual, :stderror, :vcov, :coef_table])Fitting potential
Fit using default model
fit_potential!(mpp, fdata)Molecule Pair Potential
Molecule 1 has 5 atoms (5 unique)
Molecule 2 has 1 atoms (1 unique)
Potential topology:
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** -22538.764664060964 -5.243025376695279e6 -3.2391005886259116e7 1.5156798055682138e8 551011.5920472831 2.2660963253455512e7 -5.316652440075644e7 : 1C : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 13740.236148585838 5.472515665297194e6 1.6959907070386767e8 3.752328806901236e8 -416091.7439865846 -3.998932225141039e7 -3.899070213341327e8 : 2O : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 9792.504974051504 3.139013079090014e6 7.626585584376974e7 1.3066879800125138e8 -268152.3469762912 -2.0302156130230505e7 -1.550009093303048e8 : 3O : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** -2432.4139113706888 -633362.37890601 -1.0428608883981721e7 -1.0705245941539187e7 60927.96548650013 3.458886999782353e6 1.6484328349663341e7 : 4H : 6Ar
r^-6 r^-8 r^-10 r^-12 r^-7 r^-9 r^-11 *** 4524.673108913862 858781.5222092883 7.271737286364344e6 -3.2132918849226506e6 -99324.2346945478 -3.629952540388673e6 -4.340602429711378e6 : 5H : 6Ar
or if you defined your own model
fit_potential!(model, mpp, fdata)Check root mean square deviation for potential.
rmsd(data["Points"], data["Energy"], mpp, emax=-10u"cm^-1")8.36797599293565 cm^-1We are under fitting our potential, so we can safely compare the potential to the data we used for the fitting. But it would be a good idea to confirm this, by comparing to some data that was not used for fitting.
To inspect the potential we can use use scan_potential which will calculate potential for given points and visualizes the geometry.
scan_potential(data, mpp)
You can call external programs like VMD to to visualize the data also.
# Visualize line 32 using vmd
visualize_points(data["Points"][:,32], command="vmd")Preparing CP2K input files
Geometry inputs with AtomsBase (new recommended)
To generate input data for simulations we supply a set of tools. To generate structures you can use
# structure in 86u"Å" cubic box where cluster2 has been added 1000 times
# to cluster 1
str = generate_initial_structure(data["cluster1"], data["cluster2"], 86u"Å", 1000)FlexibleSystem(Ar₁₀₀₀CH₂O₂, periodic = TTT):
bounding_box : [ 86 0 0;
0 86 0;
0 0 86]u"Å"
.-------------------------------------------------------------------------.
/| Ar |
/ | Ar Ar Ar |
/ Ar Ar Ar |
/ | Ar Ar Ar Ar Ar Arr Ar |
/Ar |AAr Ar Ar Ar Ar Ar Ar Ar Ar|
/ |Ar Ar AAr ArAr Ar Ar Ar |
/ | Arr Ar ArAr Ar Ar |
Ar ArAr| Ar AAr ArAAr Ar Ar |
/ Ar | Ar Ar Ar Ar Ar Ar ArAr Ar |
Ar | ArAr ArAArr Ar Ar Ar ArAr |
/ AAr |AAr Arr AAr Ar Ar Ar AArAr Ar Ar ArAr ArAr |
/ Ar AAr | Ar Ar Ar ArAr Ar Ar Ar Ar Ar ArrAAr |
/ Ar| Arr Arr Ar Arr AAr Ar ArAr Ar |
/ Ar ArrArArAr Ar Ar Ar Arr Ar AAr Ar Ar |
/ Ar | Ar Arr Ar AAr AAr ArAr Ar Ar Ar Ar ArAr ArAr |
/ Ar |AAr Ar Ar Ar Ar Ar Arr Ar ArArAr ArAr Ar |
/ Ar Ar ArrArr AArAr Ar Ar Ar ArrAr ArAr ArrArAr Ar Arrr Ar |
* Ar | Ar Ar Ar Arr Ar Ar Arr Ar Ar Ar |
| Ar AAr| ArAr ArAArr Ar Ar ArAr Ar ArArrrAAr Ar Ar Ar Arr Ar |
| Arr Ar AAr Ar Ar Ar ArrrAr ArArAr Ar AAr AArAr Ar ArrArAr ArAr |
| Ar ArAr Ar Ar ArArArAr Ar Ar ArArrAr Arr ArArr Ar Ar Ar |
| Ar ArrAAr Ar ArAr Ar Ar ArArr AArAr ArArAAAr ArAr |
| Ar Ar Ar| Ar ArArArr ArAr Arr ArAr ArAAr Ar AAr ArAr Ar |
| ArAAr Ar Ar ArAr Arr ArrAArArArArrArAAr ArAr |
| Ar Ar Ar AArArArr Ar Ar ArAAr Ar Ar ArAr Ar |
| Ar Ar Ar AAr ArrAr ArAr Ar AAr AArAr ArrAr Arr Ar ArrArrAr Ar ArAr |
| Ar Arr |AAr Ar Arr ArHArrr AArAr Arr Ar Ar Ar Ar |
| Ar Ar Ar ArArrAr Arr AArArH ArAr Ar AAr Ar AArr Ar Ar |
| Ar Ar ArrArrArArArArrrAr Ar Ar ArAr Ar Ar Ar |
| Ar | Ar ArArArrAr ArAr ArArAr ArrAr Ar Ar Ar Ar ArAr Ar ArAr |
| ArAr AAr Ar| Ar AAr Ar ArrAr ArAArAr Arr ArAr AAr |
| Ar |ArAr ArArAr ArArr AAArArr Ar Ar AAr Ar |
| AAr Ar AArArAr ArAr Ar Ar Ar Ar Ar Arr AAr Ar ArAr |
| ArAr Ar AAr AAr ArAr ArAr Arr ArAr Ar ArAAr Ar Ar AArArArArrAr Ar Ar |
| Ar ArAr Ar ArAr ArAr ArAr Ar Ar Arr Ar AAr Ar |
| Ar | ArAArr Ar Ar Ar Ar AAr Ar Arr Ar Arrr AAAr Ar |
| Ar Ar ArAr.-Ar--Ar------------Ar-ArAr-----Ar---AArArArAr-Ar--Ar-ArArArAr-Ar-Ar--Ar--.
| ArAr Ar ArAr AAr Ar ArAr Ar AArAr ArAAr Ar AAr Ar /
| Ar ArArr Ar AAr Ar Ar ArAAr Ar Ar AAAr Ar Ar /
| Ar Ar Ar Ar Ar ArAr AAr ArArAr Ar ArAr Ar ArAr Ar Ar AAr /
| / Ar AArr Ar Ar Ar ArAr Ar Ar Ar ArrAr /
| Arr Ar Arrr Ar Arr Ar Ar Ar ArAr /
| / ArAArAr Ar ArrArr ArAr ArAr Arr Ar Ar Ar Ar Ar /
| /Ar Ar Ar ArArArr Ar AAr Ar AAr Ar Ar Ar Ar /
| /Ar Ar Ar Ar Arr Ar ArAAr Ar Ar Ar /
| /AAr Ar Ar Ar Ar Ar Ar Ar Arr Ar /
| / Ar Ar Ar ArArAAr AAr Ar ArAr Ar /
| Ar / ArAr Ar Ar Ar /
| / Ar Ar Ar Ar AAAr Ar /
| / Ar Ar Ar Ar Ar Ar Ar /
| /Ar Ar Ar Ar Ar Ar Ar Ar Ar /
| / Ar Ar Ar Ar Ar Arr Ar Ar Ar Ar Ar /
| / Ar Ar Ar Ar Ar /
|/ Ar Ar /
*-------------------------------------------------------------------------*
You can edit the atomic symbols to reflect the potential
set_atomic_symbol!(str, :Oh, 2)
set_atomic_symbol!(str, :Oo, 3)
set_atomic_symbol!(str, :Ho, 4)
set_atomic_symbol!(str, :Hc, 5)
show(str[1:6])Atom{3, Quantity{Float64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}, Quantity{Float64, 𝐋 𝐓^-1, Unitful.FreeUnits{(a₀, s^-1), 𝐋 𝐓^-1, nothing}}, Quantity{Float64, 𝐌, Unitful.FreeUnits{(u,), 𝐌, nothing}}}[Atom(C, [ 42.6718, 43.0575, 43.2551]u"Å"), Atom(Oh, [ 43.8511, 43.3774, 42.7534]u"Å"), Atom(Oo, [ 42.1775, 42.0041, 43.0524]u"Å"), Atom(Ho, [ 44.1017, 42.7007, 42.0086]u"Å"), Atom(Hc, [ 42.1978, 43.8603, 43.9304]u"Å"), Atom(Ar, [ 60.9724, 63.212, 54.7653]u"Å")]You can then save the structure using AtomsIO
using AtomsIO
save_system("init_struct.xyz", str) # xyz-file
save_system("init_struct.pdb", str) # pdb-fileCP2K needs residue information for QM and MM parts. This can be done by using
# Save pdb file that has residue name "tfa" for atoms 1 till 5
# residue name "LIG" for other atoms
save_with_residue_data("tfa-ar-init.pdb", str, "tfa", 1:5)This file can be used as an initial file in CP2K.
Geometry inputs with Gromacs tools (old way)
First grab your favorite and make two file, one for the molecule/cluster you are studying and one for matrix and save them in PDB-format. Here we have a file for formic acid and an other for argon.
COMPND UNNAMED
AUTHOR GENERATED BY OPEN BABEL 2.3.2
HETATM 1 C tfa 1 42.585 42.840 42.933 1.00 0.00 C
HETATM 2 Oh tfa 1 43.930 42.838 42.829 1.00 0.00 O
HETATM 3 Oo tfa 1 42.014 43.738 43.531 1.00 0.00 O
HETATM 4 Ho tfa 1 44.463 43.543 43.222 1.00 0.00 H
HETATM 5 Hc tfa 1 42.008 42.039 42.484 1.00 0.00 H
CONECT 1 2 3 5
CONECT 2 1 4
CONECT 3 1
CONECT 4 2
CONECT 5 1
MASTER 0 0 0 0 0 0 0 0 5 0 5 0
ENDCOMPND UNNAMED
AUTHOR GENERATED BY OPEN BABEL 2.3.2
HETATM 6 AR LIG 2 1.472 80.636 12.825 1.00 0.00 Ar
MASTER 0 0 0 0 0 0 0 0 1 0 1 0
ENDYou need to have different residue names for QM and MM atoms, here "tfa" (trans-formic acid) and "LIG". This is demanded by CP2K.
You also need to put different identifiers to atoms at this point. Here we have:
Oh: hydroxyl group oxygenOo: carbonyl group oxygenHo: hydroxyl group hydrogenHc: hydrogen connected to carbon
Next we need to decide initial simulation box size, which depends on number of atoms in simulation. If we have 1000 argon atoms then good initial box size is 86 Å. To put the molecule in box we need extra tools. Gromacs in example has that kind of tools.
To to put the molecule into the box we use gmx editconf command
gmx editconf -f tfa.pdb -box 8.6 8.6 8.6 -o tfa-b86.pdbHere we use 86x86x86 Å box, which is ok when using 1000-matrix atoms. But you can adjust this, depending on how many matrix atoms you have.
Next we need to add argon atoms into the box. For this we use gmx insert-molecules command
gmx insert-molecules -f tfa-b86.pdb -ci ar.pdb -nmol 1000 -o tfa-ar.pdbAnd now we have the final geometry input.
CP2K input file
The best way to make CP2K input file is to split the file to several parts and using @include-commands to gather them to one file.
To do this we make
- MM-potential file
- QM-calculation file
- QMMM-boundary file
- CP2K file to gather
First we make the MM-potential file.
&MM
&FORCEFIELD
&CHARGE
ATOM Ar
CHARGE 0.0
&END CHARGE
&CHARGE
ATOM C
CHARGE 0.0
&END CHARGE
&CHARGE
ATOM Oo
CHARGE 0.0
&END CHARGE
&CHARGE
ATOM Ho
CHARGE 0.0
&END CHARGE
&CHARGE
ATOM Hc
CHARGE 0.0
&END CHARGE
&CHARGE
ATOM Oh
CHARGE 0.0
&END CHARGE
IGNORE_MISSING_CRITICAL_PARAMS .TRUE.
&NONBONDED
# Argon-argon potential from http://www.sklogwiki.org/SklogWiki/index.php/Argon
&LENNARD-JONES
ATOMS Ar Ar
EPSILON [K_e] 125.7
SIGMA [angstrom] 3.345
RCUT [angstrom] 9.0
&END LENNARD-JONES
# trans Formic acid - argon
# Just copy the potential terms from potential fit here
&GENPOT
atoms Ar C
FUNCTION Cvi/(r^6) + Cviii/(r^8) + Cx/(r^10) + Cxii/(r^12) + Cvii/(r^7) + Cix/(r^9) + Cxi/(r^11)
VARIABLES r
PARAMETERS Cvi Cviii Cx Cxii Cvii Cix Cxi
VALUES -22540.021633788096 -5.243549409354186e6 -3.2406578590178587e7 1.515360096536201e8 551050.9077903178 2.266474955203762e7 -5.3132065936126545e7
RCUT [angstrom] 9.0
&END GENPOT
&GENPOT
atoms Ar Oh
FUNCTION Cvi/(r^6) + Cviii/(r^8) + Cx/(r^10) + Cxii/(r^12) + Cvii/(r^7) + Cix/(r^9) + Cxi/(r^11)
VARIABLES r
PARAMETERS Cvi Cviii Cx Cxii Cvii Cix Cxi
VALUES 13739.083360114846 5.471838619459709e6 1.6957303994470203e8 3.7516840650039065e8 -416048.44688283757 -3.998370403083761e7 -3.898432560739321e8
RCUT [angstrom] 9.0
&END GENPOT
&GENPOT
atoms Ar Oo
FUNCTION Cvi/(r^6) + Cviii/(r^8) + Cx/(r^10) + Cxii/(r^12) + Cvii/(r^7) + Cix/(r^9) + Cxi/(r^11)
VARIABLES r
PARAMETERS Cvi Cviii Cx Cxii Cvii Cix Cxi
VALUES 9793.326640804324 3.1394020151115586e6 7.627842607574251e7 1.3069576949556419e8 -268179.8831127547 -2.0305102118835907e7 -1.550294791017888e8
RCUT [angstrom] 9.0
&END GENPOT
&GENPOT
atoms Ar Ho
FUNCTION Cvi/(r^6) + Cviii/(r^8) + Cx/(r^10) + Cxii/(r^12) + Cvii/(r^7) + Cix/(r^9) + Cxi/(r^11)
VARIABLES r
PARAMETERS Cvi Cviii Cx Cxii Cvii Cix Cxi
VALUES -2432.1617929808244 -633286.4451121971 -1.042711058845794e7 -1.070334816166878e7 60921.18782589104 3.4584354851854523e6 1.6481702154332923e7
RCUT [angstrom] 9.0
&END GENPOT
&GENPOT
atoms Ar Hc
FUNCTION Cvi/(r^6) + Cviii/(r^8) + Cx/(r^10) + Cxii/(r^12) + Cvii/(r^7) + Cix/(r^9) + Cxi/(r^11)
VARIABLES r
PARAMETERS Cvi Cviii Cx Cxii Cvii Cix Cxi
VALUES 4525.254249630937 858980.4449115618 7.2762912659367565e6 -3.2064841129619866e6 -99340.84352925561 -3.6312235927495877e6 -4.349257632528463e6
RCUT [angstrom] 9.0
&END GENPOT
&END NONBONDED
&END FORCEFIELD
&POISSON
PERIODIC XYZ
# CP2K needs ewald summation section in input. But for us it is useless,
# and you can put whatever values here.
&EWALD
EWALD_TYPE spme
ALPHA .44
GMAX 40
&END EWALD
&END POISSON
&END MMThen we make a QM-file with semi-empirical calculation method to condense the system. Here we use AM1-method that is fine for formic acid.
&DFT
BASIS_SET_FILE_NAME ${LIBDIR}/BASIS_MOLOPT
POTENTIAL_FILE_NAME ${LIBDIR}/POTENTIAL
&MGRID
NGRIDS 4
CUTOFF 350
REL_CUTOFF 50
&END MGRID
&QS
# We use semi-empirical to condence the system
METHOD AM1
&SE
&COULOMB
CUTOFF [angstrom] 10.0
&END
&EXCHANGE
CUTOFF [angstrom] 10.0
&END
&END
&END
&SCF
SCF_GUESS ATOMIC
EPS_SCF 1.0E-6 # convergence threshold for total energy
MAX_SCF 30
&OUTER_SCF
MAX_SCF 10
EPS_SCF 1.0E-6
&END
&END SCF
# Our QM-box is non periodic, so we need a Poison-solver
&POISSON
POISSON_SOLVER MT
PERIODIC NONE
&END POISSON
&END DFT
and a second file for DFT. We use BLYP-D3BJ here.
&DFT
BASIS_SET_FILE_NAME ${LIBDIR}/BASIS_MOLOPT
POTENTIAL_FILE_NAME ${LIBDIR}/POTENTIAL
&MGRID
NGRIDS 4
CUTOFF 350
REL_CUTOFF 50
&END MGRID
&QS
METHOD GPW
EPS_DEFAULT 1.0E-10
EXTRAPOLATION ASPC
&END
&SCF
SCF_GUESS ATOMIC
EPS_SCF 1.0E-6 # convergence threshold for total energy
MAX_SCF 30
&OUTER_SCF
MAX_SCF 10
EPS_SCF 1.0E-6
&END
&END SCF
&XC
&XC_FUNCTIONAL BLYP
&END XC_FUNCTIONAL
&VDW_POTENTIAL
POTENTIAL_TYPE PAIR_POTENTIAL
&PAIR_POTENTIAL
TYPE DFTD3(BJ)
R_CUTOFF 16
REFERENCE_FUNCTIONAL BLYP
PARAMETER_FILE_NAME ${LIBDIR}/dftd3.dat
&END
&END
&END XC
&POISSON
POISSON_SOLVER MT
PERIODIC NONE
&END POISSON
&END DFTThen we need to make the QM-MM file
&QMMM
CENTER_GRID TRUE
# For formic acid 10Å box is enough
&CELL
ABC [angstrom] 10 10 10
PERIODIC NONE
&END CELL
# Define QM atoms
&QM_KIND C
MM_INDEX 1
&END QM_KIND
&QM_KIND O
MM_INDEX 2 3
&END QM_KIND
&QM_KIND H
MM_INDEX 4 5
&END QM_KIND
# Apply periodic potential for MM system (default)
&PERIODIC
# We can turn multipole off, because argon has no partial charge
&MULTIPOLE OFF
&END
&END PERIODIC
&END QMMMCENTER_GRID TRUE is very important option. Without it QM system will heat up on its own and calculations will fail.
Finally we make a file that gathers all the other files. The idea here is that you only need to edit this file in the future.
@SET SYSTEM equilib
@SET LIBDIR #add path to cp2k-data directory
&GLOBAL
PROJECT ${SYSTEM}
PRINT_LEVEL LOW
RUN_TYPE MD
&END GLOBAL
&FORCE_EVAL
STRESS_TENSOR ANALYTICAL
METHOD QMMM
# These are the files we created previously
@include qm-am1.inc
@include mm.inc
@include qmmm.inc
&SUBSYS
&CELL
# box containing the system,
# using 86x86x86 box we made earlier for the inputs
ABC [angstrom] 86 86 86
&END CELL
&TOPOLOGY
COORD_FILE_NAME tfa-ar.pdb
COORD_FILE_FORMAT PDB
CONN_FILE_FORMAT USER
&GENERATE
&ISOLATED_ATOMS
# This need to span to all atoms in the simulation
# We don't have any unbreakable mm-bonds in simulation
LIST 1..1005
&END
&END
&END TOPOLOGY
&KIND Ho
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q1
ELEMENT H
&END KIND
&KIND H
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q1
ELEMENT H
&END KIND
&KIND Hc
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q1
ELEMENT H
&END KIND
&KIND Oh
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q6
ELEMENT O
&END KIND
&KIND Oo
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q6
ELEMENT O
&END KIND
&KIND O
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q6
ELEMENT O
&END KIND
&KIND C
BASIS_SET TZVP-MOLOPT-GTH
POTENTIAL GTH-BLYP-q4
&END KIND
&END SUBSYS
&END FORCE_EVAL
&MOTION
&MD
ENSEMBLE NVT
TEMPERATURE [K] 80
TEMP_TOL 50
TIMESTEP [fs] 0.5
STEPS 20000
&THERMOSTAT
REGION MASSIVE
TYPE CSVR
&CSVR
TIMECON [fs] 100
&END CSVR
&END THERMOSTAT
&END MD
&PRINT
&TRAJECTORY
&EACH
MD 20
&END EACH
FORMAT DCD
&END TRAJECTORY
&RESTART_HISTORY
&EACH
MD 5000
&END EACH
&END RESTART_HISTORY
&END PRINT
&END MOTION
Molecular dynamics
Overview here is to start from gas phase and have the system to condense to solid matrix. To do this the simulation consist of 4 phases.
- Equilibration from initial coordinates to some kind of gas.
- Condensing gas solid.
- Changing calculation method from semi-empirical to DFT and equilibrate it.
- Calculate the spectrum.
The first equilibration
Aim here is to create a super cooled gas that will compress to solid/liquid in the next phase. To do this we need to set simulation temperature to lower than boiling point. For argon 80 K is a good temperature. This can be done with the input file that was constructed earlier.
Condensing
To condense the system we need to change the dynamics to NTP, so that the external pressure will compress it. To do it we'll use following input file
@SET SYSTEM condence
@SET LIBDIR # add path to cp2k-data directory
&GLOBAL
PROJECT ${SYSTEM}
PRINT_LEVEL LOW
RUN_TYPE MD
&END GLOBAL
&FORCE_EVAL
STRESS_TENSOR ANALYTICAL
METHOD QMMM
@include qm-am1.inc
@include mm.inc
@include qmmm.inc
@include subsys.inc
&MOTION
&MD
ENSEMBLE NPT_I
TEMPERATURE [K] 20
TIMESTEP [fs] 0.5
STEPS 200000
&THERMOSTAT
REGION MASSIVE
TYPE CSVR
&CSVR
TIMECON [fs] 250
&END CSVR
&END THERMOSTAT
&BAROSTAT
PRESSURE [bar] 1.0
TEMPERATURE [K] 20
TEMP_TOL [K] 20
TIMECON [fs] 250
&END BAROSTAT
&END MD
&PRINT
&TRAJECTORY
&EACH
MD 40
&END EACH
FORMAT DCD
&END TRAJECTORY
&RESTART_HISTORY
&EACH
MD 50000
&END EACH
&END RESTART_HISTORY
&END PRINT
&END MOTIONThe rate at which the system condenses is heavily affected by thermostats coupling constant, here 250 fs. The system will condense slower, if the constant is smaller. 250 fs has proven to be a good value for many different systems.
This input file has additional file subsys.inc that includes &SUBSYSTEM section form the previous run. You can get the section by using grep on restart file.
grep -A 10000 "&SUBSYS"In this phase we also set the final temperature, now 20 K.
Change to DFT
Next we'll change QM calculation method to DFT. To do this we'll use slightly modified input file from the previous phase
@SET SYSTEM dftequilib
@SET LIBDIR # add path to cp2k-data directory
&GLOBAL
PROJECT ${SYSTEM}
PRINT_LEVEL LOW
RUN_TYPE MD
&END GLOBAL
&FORCE_EVAL
STRESS_TENSOR ANALYTICAL
METHOD QMMM
@include qm-blyp-d3bj.inc
@include mm.inc
@include qmmm.inc
@include condensed_subsys.inc
&MOTION
&MD
ENSEMBLE NPT_I
TEMPERATURE [K] 20
TIMESTEP [fs] 0.5
# You can increase this if needed
STEPS 10000
&THERMOSTAT
REGION MASSIVE
TYPE CSVR
&CSVR
# This constant is not that important anymore
TIMECON [fs] 25
&END CSVR
&END THERMOSTAT
&BAROSTAT
PRESSURE [bar] 1.0
TEMPERATURE [K] 20
TEMP_TOL [K] 20
TIMECON [fs] 250
&END BAROSTAT
&END MD
&PRINT
&TRAJECTORY
&EACH
MD 40
&END EACH
FORMAT DCD
&END TRAJECTORY
&RESTART_HISTORY
&EACH
MD 5000
&END EACH
&END RESTART_HISTORY
&END PRINT
&END MOTIONIR spectrum calculation
To calculate spectrum we need dipole moments, to do this we need to add command to print them to our QM-file
&DFT
BASIS_SET_FILE_NAME ${LIBDIR}/BASIS_MOLOPT
POTENTIAL_FILE_NAME ${LIBDIR}/POTENTIAL
&MGRID
NGRIDS 4
CUTOFF 350
REL_CUTOFF 50
&END MGRID
&QS
METHOD GPW
EPS_DEFAULT 1.0E-10
EXTRAPOLATION ASPC
&END
&SCF
SCF_GUESS ATOMIC
EPS_SCF 1.0E-6 # convergence threshold for total energy
MAX_SCF 30
&OUTER_SCF
MAX_SCF 10
EPS_SCF 1.0E-6
&END
&END SCF
&XC
&XC_FUNCTIONAL BLYP
&END XC_FUNCTIONAL
&VDW_POTENTIAL
POTENTIAL_TYPE PAIR_POTENTIAL
&PAIR_POTENTIAL
TYPE DFTD3(BJ)
R_CUTOFF 16
REFERENCE_FUNCTIONAL BLYP
PARAMETER_FILE_NAME ${LIBDIR}/dftd3.dat
&END
&END
&END XC
&POISSON
POISSON_SOLVER MT
PERIODIC NONE
&END POISSON
&PRINT
&MOMENTS
PERIODIC FALSE
&EACH
MD 1
&END
MAX_MOMENT 1
FILENAME =dipole.traj
&END MOMENTS
&END
&END DFTWe'll also need to edit input file to change the mode to NVE
@SET SYSTEM spectrum
@SET LIBDIR # add path to cp2k-data directory
&GLOBAL
PROJECT ${SYSTEM}
PRINT_LEVEL LOW
RUN_TYPE MD
&END GLOBAL
&FORCE_EVAL
STRESS_TENSOR ANALYTICAL
METHOD QMMM
@include qm-blyp-d3bj-dipoles.inc
@include mm.inc
@include qmmm.inc
@include dft_subsys.inc
&MOTION
&MD
ENSEMBLE NVE
TIMESTEP [fs] 0.5
STEPS 80000
&END MD
&PRINT
&TRAJECTORY
&EACH
MD 5
&END EACH
FORMAT DCD
&END TRAJECTORY
&RESTART_HISTORY
&EACH
MD 5000
&END EACH
&END RESTART_HISTORY
&END PRINT
&END MOTIONThis will create dipole.traj-file that contains dipole moments. You can use IRSpectrum.jl to calculate IR-spectrum form the dipole trajectory file.