Proposing a new model for ramp compression from ab initio calculations

High-pressure states of matter can be reached through static compression, using diamond

anvil cells, or by dynamic shock and ramp compression experiments. While shock

compression is relatively well understood and described by the formalism of the Hugoniot

equations, no such formalism exists for ramp compression. The compression is thought to

be quasi-isentropic, leading to lower temperatures than shock compression, but there are

currently no measurements of temperature during ramp compression or a theoretical

framework to derive how much heating occurs. In this work, we present a model of ramp

compression that is based on thermodynamics and ab initio calculations where we

approximate ramp loading as a series of compression and relaxation steps. We apply our

model to diamond and we compare our predictions with the measured stress-density

relations reported from experiments [1-3]. We find good agreement between our model and

a multishock Hugoniot scheme, as well as with a recently proposed strength model for

diamond based on plastic work [4].

References:

[1] D. Bradley et al., PRL 102, 075503 (2009).

[2] R. Smith et al., Nature 511, 330 (2014).

[3] A. Lazicki et al., Nature 589, 532 (2021).

[4] D.C. Swift et al., arXiv 2004.03071 (2020).