Molecula dynamcs modelng of hemal and mechancal popees Alejando Sachan School of Maeals Engneeng Pudue Unvesy sachan@pudue.edu
Maeals a molecula scales Molecula maeals Ceamcs Meals
Maeals popees chas Maeals look vey dffeen Maeals popees vay by many odes of magnude Composon/chemsy Mcosucue A vaey of mechansms goven maeals behavo Maeals Selecon n Mechancal Desgn (3d edon) by MF Ashby, Buewoh Henemann, 2005
Mulscale modelng of maeals Undesand he molecula level ogns of maeals behavo Pedc he behavo of maeals fom fs pncples T m e second mcosec nanosec. pcosec. Elecons Aoms Mesopacles Elemens Quanum Mechancs Molecula dynamcs Mesoscale Macoscale femosec. L e n g h nanomee mcon mm mees Help desgn new maeals o devces wh mpoved pefomance
Molecula dynamcs Explcly solve he dynamcs of all aoms of he maeal of nees Newon s equaons of moon wh foces obaned fom he ne-aomc poenal
MD: sucue of an MD code Inal condons [ (0), v (0)] Calculae foces a cuen me [F ()] fom () Inegae equaons of moon () _ (+Δ) v() _ v(+δ) _+Δ Save popees Oupu fle Done? Y End No
MD: negang he equaons of moon MD: negang he equaons of moon ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 4 3 2 4 3 2 6 1 2 1 6 1 2 1 + Ο Δ Δ Δ + Δ Δ + Ο Δ Δ + Δ + Δ + + Δ &&& && & &&& && & Taylo expanson of posons wh me The Vele algohm
MD: hemodynamc ensembles & u& u F m wh F R E 3 2 Tempeaue: ( ) 2 NkT K mu ( ) me 1 2 N 1 me Insananeous empeaue (T * ): 3 2 NkT * 1 2 ( ) ( ) 2 K mu ( ) N 1
MD: sohemal molecula dynamcs MD: sohemal molecula dynamcs m F u u & & Beendsen s hemosa Nose-Hoove hemosa m F u u & & How can we modfy he EoM so ha hey lead o consan empeaue?
MD applcaons: melng Smples and mos dec appoach: Take a sold and hea up a consan pessue unl mels Then cool he mel unl e-cysalzes Poblems Supeheang of he sold & undecoolng of he lqud Why? Luo e al. PRB 68, 134206 (2003)
MD applcaons: melng 2-phase MD smulaons Place lqud and sold n one cell Run NPT smulaons a vaous T
MD applcaons: melng 2-phase MD smulaon Melng a amben pessue Smulaon: 3150±50 K (4%) Expemen: 3290±50 K Pessue (GPa) Band elecons Cohen ab no Hugono Usng expe. pessue 2-phase MD smulaon Expemen shock melng Bown and Shane (1984) Tempeaue fo Hugono Fee elecons Tempeaue (K)
MD applcaons: nano-mechancs of defomaon Mechansms of plasc defomaon Maeals sengh Slp plane Edge dslocaon Scew dslocaon Buges veco
MD applcaons: nano-mechancs of defomaon nal ε0.0 plasc elasc defomaon defomaon ε0.07 ε0.09 ε0.59 ε0.74
MD applcaons: nano-mechancs of defomaon Pson NAl age NAl alloy: plasc defomaon nduced by shock compesson MD enables a dealed chaacezaon of he mechansms of plasc defomaon
MD applcaons: condensed-mae chemsy Plasc bonded explosves Enegec maeal pacles n a ubbey bnde C-NO 2 (TATB, TNT) N-NO 2 (HMX, RDX) O-NO 2 (PETN) O 2 N N RDX NO 2 Seconday explosves (nal eacons ae endohemc) Sensvy o undesed deonaon N N NO 2 Popellans Namne used n popellan composes Seconday HE _ exohemc eacons fa fom he suface _ lowe empeaue a bun suface Lage specfc mpulse (Isp) Themal and shock nduced decomposon and eacon of hgh enegy maeals
MD applcaons: decomposon of RDX Shock decomposon 32 RDX molecules on 32 RDX molecules u Sachan e al. Phys. Rev. Le. (2003) p u p Themal decomposon
MD applcaons: compuaonal maeals desgn Polyme-based nano-acuao Make use of sucual anson o acheve lage sans All ans bonds san T and G bonds All ans bonds Elecc feld Zeo feld Elecc feld Sachan and Goddad, Appl. Phys. Le (2005)
Mesoscale: : beyond MD All aom MD s vey expensve Pacles wh long ange neacons (elecosacs) Sho me sep necessay C-H bond vbaonal peod ~10 fs 10-14 s MD me-sep: <1 fs MD s always classcal (C V ~3Nk) Mesodynamcs Mesopacles epesen goups of aoms Molecules o gans n a polycysallne sold (B.L. Holan) Mesopoenal (effecve neacons beween mesopacles) Themal ole of mplc degees of feedom
Mesoscale: : empeaue se dung shock loadng Tes case: shock on a cysallne polyme me0.8 ps me1.6 ps All aom MD smulaon Inenal Molecula me3.2 ps Molecula: c.m. velocy of molecules aound anslaon Inenal: aomc veloces aound c.m. vel. of molecules
Mesoscale: : lmaon of adonal appoach Enegy ncease due o shockwave descbed accuaely Reduced numbe of modes o shae he enegy Lage oveesmaon of empeaue
Mesoscale: : new appoach Local mesopacle velocy: < u Local mesopacle empeaue: Equaons of moon: & u + χf F u& η u < u > m Change n mesopacle enegy: > ( ) 3kT j meso m u j j j j m w ( j) ( ) w j m < > j j u j u w j ( ) j 2 ( ) w j wegh dsance Change n nenal enegy so ha oal enegy s conseved:
Mesoscale: : New equaons of moon Allow enegy exchange beween mesopacles and nenal DoFs Couple local meso empeaue wh nenal empeaue & u& E& n u F m + χ F T& χf C n n F T χ γ meso T T 0 n Couple hough he poson updae equaon Key feaues Toal enegy (meso + nenal) s conseved c.m. velocy s conseved Gallean nvaan Coec descpon of he ballsc egme Sachan and Holan (PRL, Jan 2005) Fne hemosas
Mesodynamcs: : hemodynamcally accuae Themodynamcally accuae mesoscale descpon Themal ole of mplc degees of feedom descbed by he specfc hea Can ncopoae C V based on quanum sascal mechancs
Runnng MD @ nanohub The Newok fo Compuaonal Nanoechnology a Pudue developed he nanohub (www.nanohub.og) nanohub povdes onlne sevces fo eseach, educaon and collaboaon The maeals smulaon oolk a nanohub Developed by he Sachan goup Enables unnng eal MD smulaons usng smply a webbowse All you have o do s egse o he nanohub (pefeably befoe lab sesson)