###### Abstract  
Chromium possesses remarkable physical properties such as hardness and corrosion resistance. Chromium is also a very important geophysical material as it is assumed that lighter Cr isotopes were dissolved in the Earth's molten core during the planet's formation, which makes Cr one of the main constituents of the Earth's core. Unfortunately, Cr has remained one of the least studied \(3d\) transition metals. In a very recent combined experimental and theoretical study ([PERSON] et al., Scientific Reports, 2022), the equation of state and melting curve of chromium were studied to 150 GPa, and it was determined that the ambient body-centered cubic (bcc) phase of crystalline Cr remains stable in the whole pressure range considered. However, the importance of the knowledge of the physical properties of Cr, specifically its phase diagram, necessitates further study of Cr to higher pressure. In this work, using a suite of ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid-solid phase transition boundaries, we obtain the theoretical phase diagram of Cr to 2.5 TPa. We calculate the melting curves of the two solid phases that are present on its phase diagram, namely, the lower-pressure bcc and the higher-pressure hexagonal close-packed (hcp) ones, and obtain the equation for the bcc-hcp solid-solid phase transition boundary. We also obtain the thermal equations of state of both bcc-Cr and hcp-Cr, which are in excellent agreement with both experimental data and QMD simulations. We argue that 2180 K as the value of the ambient melting point of Cr which is offered by several public web resources (\"Wikipedia,\" \"WebElements,\" \"It's Elemental,\" etc.) is most likely incorrect and should be replaced with 2135 K, found in most experimental studies as well as in the present theoretical work. a 2022  
found in [1]. Using Cr isotope measurements from both the meteorites and the Earth's crust, it was shown [1] that lighter Cr isotopes sank into the Earth's core during the planet's formation. In addition, first-principles-based computer simulations revealed [1] that this process occurred in the early stages of the Earth's formation when smaller bodies were coalescing to form the contemporary Earth. Thus, the knowledge of the physical properties of chromium is very important for materials science and condensed matter physics as well as for geophysics, since being one of the main constituents of the Earth's core, its physical properties are directly related to the Earth's thermal history. Unfortunately, chromium has remained one of the least studied \(3d\) transition metals. Most of the information on its physical properties is available at low pressure (\(P\)) only. Its crystal structure at ambient conditions is body-centered cubic (bcc). With decreasing temperature (\(T\)), bcc is modified by two first-order phase transitions: to antiferromagnetic (AF) phase with orthorhombically distorted bcc at the Neel \(T\) (\(T_{\rm N}\)) of 311 K, and to AF phase with tetragonally distorted bcc at the spin-flip \(T\) of 123 K [2]. In both phases, the bcc distortions are too small to be detected by X-ray diffraction. The physical reasons for the ground state of Cr being AF have been discussed in several papers; see, e.g., Ref. [3], which provides arguments for bcc-Fe being ferromagnetic (FM) but both bcc-Mn and bcc-Cr being AF. Above 311 K, Cr is paramagnetic (PM). With increasing \(P\), chromium is expected to exhibit a polymorphism, similar to both molybdenum and tungsten, its partners in Period 6B of the periodic table (PT), the high-\(P\) crystal structure of which is double-hexagonal-close-packed (double-hcp, or dhcp) [4]. Indeed, a solid-solid (s-s) phase transition into hcp is predicted theoretically for Cr, but the values of the transition \(P\) that can be found in the literature span an interval of 7-12.5 Mbar [5].