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using namespace std; |
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namespace OpenMD { |
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|
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/* GB is the Gay-Berne interaction for ellipsoidal particles. The original |
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* paper (for identical uniaxial particles) is: |
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* J. G. Gay and B. J. Berne, J. Chem. Phys., 74, 3316-3319 (1981). |
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* A more-general GB potential for dissimilar uniaxial particles: |
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* D. J. Cleaver, C. M. Care, M. P. Allen and M. P. Neal, Phys. Rev. E, |
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* 54, 559-567 (1996). |
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* Further parameterizations can be found in: |
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* A. P. J. Emerson, G. R. Luckhurst and S. G. Whatling, Mol. Phys., |
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* 82, 113-124 (1994). |
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* And a nice force expression: |
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* G. R. Luckhurst and R. A. Stephens, Liq. Cryst. 8, 451-464 (1990). |
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* Even clearer force and torque expressions: |
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* P. A. Golubkov and P. Y. Ren, J. Chem. Phys., 125, 64103 (2006). |
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* New expressions for cross interactions of strength parameters: |
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* J. Wu, X. Zhen, H. Shen, G. Li, and P. Ren, J. Chem. Phys., |
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* 135, 155104 (2011). |
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* |
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* In this version of the GB interaction, each uniaxial ellipsoidal type |
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* is described using a set of 6 parameters: |
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* d: range parameter for side-by-side (S) and cross (X) configurations |
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* l: range parameter for end-to-end (E) configuration |
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* epsilon_X: well-depth parameter for cross (X) configuration |
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* epsilon_S: well-depth parameter for side-by-side (S) configuration |
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* epsilon_E: well depth parameter for end-to-end (E) configuration |
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* dw: "softness" of the potential |
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* |
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* Additionally, there are two "universal" paramters to govern the overall |
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* importance of the purely orientational (nu) and the mixed |
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* orientational / translational (mu) parts of strength of the interactions. |
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* These parameters have default or "canonical" values, but may be changed |
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* as a force field option: |
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* nu_: purely orientational part : defaults to 1 |
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* mu_: mixed orientational / translational part : defaults to 2 |
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*/ |
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|
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GB::GB() : name_("GB"), initialized_(false), mu_(2.0), nu_(1.0), forceField_(NULL) {} |
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GayBerneParam GB::getGayBerneParam(AtomType* atomType) { |
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simError(); |
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} |
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< |
RealType d1, l1, e1, er1, dw1; |
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RealType d1, l1, eX1, eS1, eE1, dw1; |
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if (atomType->isGayBerne()) { |
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GayBerneParam gb1 = getGayBerneParam(atomType); |
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d1 = gb1.GB_d; |
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l1 = gb1.GB_l; |
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e1 = gb1.GB_eps; |
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er1 = gb1.GB_eps_ratio; |
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eX1 = gb1.GB_eps_X; |
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eS1 = gb1.GB_eps_S; |
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eE1 = gb1.GB_eps_E; |
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dw1 = gb1.GB_dw; |
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} else if (atomType->isLennardJones()) { |
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d1 = getLJSigma(atomType) / sqrt(2.0); |
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e1 = getLJEpsilon(atomType); |
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l1 = d1; |
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< |
er1 = 1.0; |
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eX1 = getLJEpsilon(atomType); |
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eS1 = eX1; |
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eE1 = eX1; |
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dw1 = 1.0; |
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} else { |
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sprintf( painCave.errMsg, |
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AtomType* atype2 = (*it).second; |
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RealType d2, l2, e2, er2, dw2; |
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RealType d2, l2, eX2, eS2, eE2, dw2; |
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if (atype2->isGayBerne()) { |
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GayBerneParam gb2 = getGayBerneParam(atype2); |
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d2 = gb2.GB_d; |
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l2 = gb2.GB_l; |
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e2 = gb2.GB_eps; |
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er2 = gb2.GB_eps_ratio; |
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eX2 = gb2.GB_eps_X; |
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eS2 = gb2.GB_eps_S; |
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eE2 = gb2.GB_eps_E; |
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dw2 = gb2.GB_dw; |
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} else if (atype2->isLennardJones()) { |
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d2 = getLJSigma(atype2) / sqrt(2.0); |
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e2 = getLJEpsilon(atype2); |
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l2 = d2; |
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er2 = 1.0; |
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eX2 = getLJEpsilon(atype2); |
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eS2 = eX2; |
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eE2 = eX2; |
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dw2 = 1.0; |
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} |
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// assumed LB mixing rules for now: |
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mixer1.dw = 0.5 * (dw1 + dw2); |
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< |
mixer1.eps0 = sqrt(e1 * e2); |
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mixer1.eps0 = sqrt(eX1 * eX2); |
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mixer2.dw = mixer1.dw; |
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mixer2.eps0 = mixer1.eps0; |
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RealType mi = RealType(1.0)/mu_; |
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< |
RealType er = sqrt(er1 * er2); |
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RealType ermu = pow(er, (RealType(1.0) / mu_)); |
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RealType xp = (1.0 - ermu) / (1.0 + ermu); |
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RealType ap2 = 1.0 / (1.0 + ermu); |
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mixer1.xp2 = xp * xp; |
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mixer1.xpap2 = xp * ap2; |
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mixer1.xpapi2 = xp / ap2; |
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mixer1.xpap2 = (pow(eS1, mi) - pow(eE1, mi)) / (pow(eS1, mi) + pow(eE2, mi)); |
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mixer1.xpapi2 = (pow(eS2, mi) - pow(eE2, mi)) / (pow(eS2, mi) + pow(eE1, mi)); |
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mixer1.xp2 = (pow(eS1, mi) - pow(eE1, mi)) * (pow(eS2, mi) - pow(eE2, mi)) / |
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(pow(eS2, mi) + pow(eE1, mi)) / (pow(eS1, mi) + pow(eE2, mi)) ; |
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// xpap2 and xpapi2 for j-i pairs are reversed from the same i-j pairing. |
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// Swapping the particles reverses the anisotropy parameters: |
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mixer2.xpap2 = mixer1.xpapi2; |
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mixer2.xpapi2 = mixer1.xpap2; |
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mixer2.xp2 = mixer1.xp2; |
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mixer2.xpap2 = mixer1.xpap2; |
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mixer2.xpapi2 = mixer1.xpapi2; |
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// only add this pairing if at least one of the atoms is a Gay-Berne atom |
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RealType xpap2 = mixer.xpap2; |
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RealType xpapi2 = mixer.xpapi2; |
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// cerr << "atypes = " << idat.atypes.first->getName() << " " << idat.atypes.second->getName() << "\n"; |
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// cerr << "sigma0 = " <<mixer.sigma0 <<"\n"; |
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// cerr << "dw = " <<mixer.dw <<"\n"; |
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// cerr << "eps0 = " <<mixer.eps0 <<"\n"; |
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// cerr << "x2 = " <<mixer.x2 <<"\n"; |
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// cerr << "xa2 = " <<mixer.xa2 <<"\n"; |
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// cerr << "xai2 = " <<mixer.xai2 <<"\n"; |
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// cerr << "xp2 = " <<mixer.xp2 <<"\n"; |
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// cerr << "xpap2 = " <<mixer.xpap2 <<"\n"; |
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// cerr << "xpapi2 = " <<mixer.xpapi2 <<"\n"; |
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|
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Vector3d ul1 = idat.A1->getRow(2); |
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Vector3d ul2 = idat.A2->getRow(2); |
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// cerr << "ul1 = " <<ul1<<"\n"; |
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// cerr << "ul2 = " <<ul2<<"\n"; |
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|
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RealType a, b, g; |
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bool i_is_LJ = idat.atypes.first->isLennardJones(); |
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RealType au2 = au * au; |
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RealType bu2 = bu * bu; |
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RealType g2 = g * g; |
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RealType H = (xa2 * au2 + xai2 * bu2 - 2.0*x2*au*bu*g) / (1.0 - x2*g2); |
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RealType Hp = (xpap2*au2 + xpapi2*bu2 - 2.0*xp2*au*bu*g) / (1.0 - xp2*g2); |
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// cerr << "au2 = " << au2 << "\n"; |
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// cerr << "bu2 = " << bu2 << "\n"; |
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// cerr << "g2 = " << g2 << "\n"; |
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// cerr << "H = " << H << "\n"; |
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// cerr << "Hp = " << Hp << "\n"; |
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|
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RealType sigma = sigma0 / sqrt(1.0 - H); |
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RealType e1 = 1.0 / sqrt(1.0 - x2*g2); |
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RealType e2 = 1.0 - Hp; |
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RealType s3 = sigma*sigma*sigma; |
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RealType s03 = sigma0*sigma0*sigma0; |
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// cerr << "vdwMult = " << *(idat.vdwMult) << "\n"; |
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// cerr << "eps = " << eps <<"\n"; |
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// cerr << "mu = " << mu_ << "\n"; |
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// cerr << "R12 = " << R12 << "\n"; |
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// cerr << "R6 = " << R6 << "\n"; |
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// cerr << "R13 = " << R13 << "\n"; |
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// cerr << "R7 = " << R7 << "\n"; |
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// cerr << "e2 = " << e2 << "\n"; |
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// cerr << "rij = " << *(idat.rij) << "\n"; |
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// cerr << "s3 = " << s3 << "\n"; |
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// cerr << "s03 = " << s03 << "\n"; |
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// cerr << "dw = " << dw << "\n"; |
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|
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RealType pref1 = - *(idat.vdwMult) * 8.0 * eps * mu_ * (R12 - R6) / |
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(e2 * *(idat.rij)); |
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|
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(1.0 - xp2 * g2) / e2 + 8.0 * eps * s3 * (3.0 * R7 - 6.0 * R13) * |
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(x2 * au * bu - H * x2 * g) / (1.0 - x2 * g2) / (dw * s03); |
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// cerr << "pref = " << pref1 << " " << pref2 << "\n"; |
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// cerr << "dU = " << dUdr << " " << dUda <<" " << dUdb << " " << dUdg << "\n"; |
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|
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Vector3d rhat = *(idat.d) / *(idat.rij); |
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Vector3d rxu1 = cross(*(idat.d), ul1); |
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Vector3d rxu2 = cross(*(idat.d), ul2); |
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*(idat.t2) += (dUdb * rxu2 + dUdg * uxu) * *(idat.sw); |
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*(idat.vpair) += U; |
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|
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// cerr << "f1 term = " << (dUdr * rhat + dUda * ul1 + dUdb * ul2) * *(idat.sw) << "\n"; |
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// cerr << "t1 term = " << (dUda * rxu1 - dUdg * uxu) * *(idat.sw) << "\n"; |
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// cerr << "t2 term = " << (dUdb * rxu2 + dUdg * uxu) * *(idat.sw) << "\n"; |
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// cerr << "vp term = " << U << "\n"; |
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|
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return; |
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} |
