The Isotope-Effect in the Phase Transition of KH(2)PO(4): New Insights from Ab Initio Path-Integral Simulations
The Isotope-Effect in the Phase Transition of KH(2)PO(4): New Insights from Ab Initio Path-Integral Simulations
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KH(2)PO(4) 相变中的同位素效应：从头算路径积分模拟的新见解
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
D. Sebastiani
中科院分区：
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作者：
Varadharajan Srinivasan;D. Sebastiani
研究了准电相磷酸二氢钾（KDP）晶体对称低势垒氢键中1H和2H同位素的量子力学定位。这些氢原子的空间密度分布被怀疑是KDP铁电相变中观察到的惊人的大同位素效应的原因。我们采用从头算路径积分分子动力学模拟得到了1H和2H的核实空间和动量空间密度n(R)和n(k)，并将后者的密度与实验中子康普顿散射数据进行了比较。我们的结果表明，两种同位素在KDP的准电相性质上存在质的差异。虽然这两种准电态都是由量子离域产生的，但本质上的区别是氢原子在氢键上的隧道行为从可能相干到非相干的变化。
We investigate the quantum-mechanical localization of 1H and 2H isotopes in the symmetric low-barrier hydrogen-bonds of potassium dihydrogen phosphate (KDP) crystals in the paraelectric phase. The spatial density distributions of these hydrogen atoms are suspected to be responsible for the surprisingly large isotope effect observed for the ferroelectric phase transition in KDP. We employ ab initio path integral molecular dynamics simulations to obtain the nuclear real-space and momentum-space densities n(R) and n(k) of 1H and 2H, of which the latter densitites are compared to experimental neutron compton scattering data. Our results suggest a qualitative difference in the nature of the paraelectric phase in KDP between the two isotopes. Whereas both paraelectric states result from quantum delocalization, the essential difference is the change from a probably coherent to incoherent tunneling behavior of the hydrogen atoms across the hydrogen-bonds.